The martyrdom of Hazrat Mohsen

Isn't the martyrdom of Hazrat Mohsen (peace be upon him) in contrast with the remark of the prophet (peace of Allah be upon him and his descendants) that said to Hazrat Zahra (peace be upon her) '' you are the first person from my Ahle Beit that will join me''.
According to the Sunni and Shiite narration, Hazrat Fateme (peace be upon her) was the first person from Ahle Beit that joined the messenger of God (peace of Allah be upon him and his descendants) after his decease.
On the other hand, according to the claim of Shias, martyred Mohsen is the brother of Hassan and Hussein and the son of Hazrat Fateme (peace be upon her). In other words, she is from Ahle Beit (peace be upon them), but she died sooner than her mother.
Has the messenger of God made a mistake or there was no person with the name '' Mohsen''?
The criticism and analysis
There is no question that Hazrat Mohsen (peace be upon him) was martyred. There are a lot of narrations in the Shiite and Sunni books that confirm this matter. We will mention these narrations in a separate article for dear readers.
On the other hand, as you referred, this matter, Hazrat Zahra (peace be upon her) was the first person from Ahle Beit that joined the messenger of God, has been confirmed. But how can we remove the considered contrast? We should answer:
The word '' Ahle Beit '' has been used in all of these narrations and the prophet said '' you are the first person from Ahle Beit will join me'' and according to the remark of the prophet, Ahle Beit is attributed to persons that God will purify them from any kinds of vices according to the verse of Tathir and the messenger of God (peace of Allah be upon him and his descendants) and in fact, the messenger of God ( peace of Allah be upon him and his descendants) interpreted the word '' Ahle Beit'' and he has devoted it to these persons.
This matter can be proved with over seventy narrations in the Sunni books.
Hence, the word '' Ahle Beit'' includes the companions of Kasa in the time of the messenger of God (peace of Allah be upon him and his descendants) and it will not include someone else such as: Hazrat Mohsen, Hazrat Zeinab and …and the women of the prophet or someone else.

The narrations that the messenger of God (peace of Allah be upon him and his descendants) annunciated to Hazart Zahra (peace be upon her) are the following cases. We will mention several narrations from the Shiite and Sunni books due to briefness:
Sheikh Mofid has written
فَجَاءَتِ الرِّوَایَةُ أَنَّهُ قِیلَ لِفَاطِمَةَ (علیها السلام) مَا الَّذِی أَسَرَّ إِلَیْكِ رَسُولُ اللَّهِ (صلی الله علیه وآله وسلم) فَسُرِیَ عَنْكِ مَا كُنْتِ عَلَیْهِ مِنَ الْحَزَنِ وَ الْقَلَقِ بِوَفَاتِهِ قَالَتْ إِنَّهُ خَبَّرَنِی أَنَّنِی أَوَّلُ أَهْلِ بَیْتِهِ لُحُوقاً بِهِ وَ أَنَّهُ لَنْ تَطُولَ الْمُدَّةُ بِی بَعْدَهُ حَتَّى أُدْرِكَهُ فَسُرِیَ ذَلِكَ عَنِّی.
Hazrat Fateme (peace be upon her) was asked '' what secret did the messenger of God (peace of Allah be upon him and his descendants) say that it caused that the grief of his death did not suffer you, you anxiety decreased and your face became red? She said '' the messenger of God (peace of Allah be upon him and his descendants) informed me '' you are the first person from my Ahle Beit that will join me and you will not live for a long time after me''.
This news made me happy and decreased my grief.
Al-Sheikh Al-Mofid Muhammad Ben Muhammad Ben Al-Naman Ibn Al-Moalem Abi Abdullah Al-Akbari, Al-Baghdadi (died in 413 Hejira), Al-Ershad Fi Marefat Hojajollah Ali Al-Ebad , v 1 p 187, Researched by: Ale Al-Beit Alaihem Al-Salam Le Tahghigh Al-Torath Institute, Published by: Dar Al-Mofid Leltabaat Al-Nashr Al-Tozi, Beirut, Lebanon, Second Edition 1414 Hejira- 1993
Al-Majlesi, Alame Sheikh Muhammad Bagher (died in 1111 Hejira), Bahar Al-Anvar Al-Jameat Ledorer Akhbar Al-Aeme Al-Athar, v 22 p 470, Published by: Al-Vafa Institute, Beirut, Second Edition; Al-Mosahahat, 1403 Hejira- 1983

Ibn Jarir Tabari Shiei has written
عن أبی بصیر، عن أبی عبد الله ( علیه السلام )، قال: لما قبض رسول الله ( صلى الله علیه وآله ) ما ترك إلا الثقلین، كتاب الله وعترته أهل بیته، وكان قد أسر إلى فاطمة ( صلوات الله علیها ) أنها لاحقة به، وأنها أول أهل بیته لحوقا.
Imam Sadegh (peace be upon him) said '' when the prophet passed away, he left two precious companions and jewelry, one of them is the book of God and the other one is my Etrat and Ahle Beit. Then he said to Fateme '' you will join me''. The first person from Ahle Beit that joined the prophet was Fateme.
Al-Tabari, Al-Sheikh Abi Jafar Muhammad Ben Jarir Ben Rostam (died in 4th Century), Dalael Al-Emamat, p 131, Researched by: Ghasam Al-Dorasat Al-Eslamiye, Al-Bethat Institute, Published by: Markaz Al-Tabaat va Al-Nashr Fi Al-Bethat Institute, Qom, First Edition; 1413 hejira
This matter can be seen in the Sunni books.
Muhammad Bin Ismaeil Bokhari has written

حَدَّثَنَا أَبُو نُعَیْمٍ حَدَّثَنَا زَكَرِیَّاءُ عَنْ فِرَاسٍ عَنْ عَامِرٍ الشَّعْبِیِّ عَنْ مَسْرُوقٍ عَنْ عَائِشَةَ رَضِیَ اللَّهُ عَنْهَا قَالَتْ أَقْبَلَتْ فَاطِمَةُ تَمْشِی كَأَنَّ مِشْیَتَهَا مَشْیُ النَّبِیِّ صَلَّى اللَّهُ عَلَیْهِ وَسَلَّمَ فَقَالَ النَّبِیُّ صَلَّى اللَّهُ عَلَیْهِ وَسَلَّمَ مَرْحَبًا بِابْنَتِی ثُمَّ أَجْلَسَهَا عَنْ یَمِینِهِ أَوْ عَنْ شِمَالِهِ ثُمَّ أَسَرَّ إِلَیْهَا حَدِیثًا فَبَكَتْ فَقُلْتُ لَهَا لِمَ تَبْكِینَ ثُمَّ أَسَرَّ إِلَیْهَا حَدِیثًا فَضَحِكَتْ فَقُلْتُ مَا رَأَیْتُ كَالْیَوْمِ فَرَحًا أَقْرَبَ مِنْ حُزْنٍ فَسَأَلْتُهَا عَمَّا قَالَ فَقَالَتْ مَا كُنْتُ لِأُفْشِیَ سِرَّ رَسُولِ اللَّهِ صَلَّى اللَّهُ عَلَیْهِ وَسَلَّمَ حَتَّى قُبِضَ النَّبِیُّ صَلَّى اللَّهُ عَلَیْهِ وَسَلَّمَ فَسَأَلْتُهَا فَقَالَتْ أَسَرَّ إِلَیَّ إِنَّ جِبْرِیلَ كَانَ یُعَارِضُنِی الْقُرْآنَ كُلَّ سَنَةٍ مَرَّةً وَإِنَّهُ عَارَضَنِی الْعَامَ مَرَّتَیْنِ وَلا أُرَاهُ إِلا حَضَرَ أَجَلِی وَإِنَّكِ أَوَّلُ أَهْلِ بَیْتِی لَحَاقًا بِی فَبَكَیْتُ فَقَالَ أَمَا تَرْضَیْنَ أَنْ تَكُونِی سَیِّدَةَ نِسَاءِ أَهْلِ الْجَنَّةِ أَوْ نِسَاءِ الْمُؤْمِنِینَ فَضَحِكْتُ لِذَلِكَ.
Aeshe says '' Fateme that walked the same as her father came to the messenger of God (peace of Allah be upon him and his descendants). The prophet said '' welcome my daughter''. He had her sit in his left or right side and then he talked slowly. Fateme started crying. I said '' why are you crying?'' he talked slowly once more and Feteme became happy. I have never seen happiness and grief together. I asked Fateme its reason. She said '' I never reveal the secret of the prophet of God. After the messenger of God (peace of Allah be upon him and his descendants), I asked it again and she said '' my father said '' Gabriel presented Quran to me once a year, but he presented to me twice this year. It seems my death is about to happen and you, my father, are the first person that will join me. In such time, I cried. He said '' don't you like to be the master of the women of the heaven and the devout woman; therefore, I laughed
Al-Bokhari Al-Jaafi, Muhammad Ben Esmaeel Abu Abdullah (died in 256 Hejira), Sahih Al-Bokhari, v 3 p 1326, hadith 3426, Researched by: D. Mostafa Deib Al-Bagha, Published by: Dar Ibn Kathir, Al-Yamame, Beirut, Third Edition; 1407 Hejira- 1987

Tabarani has written in the book '' Majam Kabir''
عن عَائِشَةَ قالت قلت لِفَاطِمَةَ بنتِ رسول اللَّهِ صلى اللَّهُ علیه وسلم رَأَیْتُكِ أَكْبَبْتِ على النبی صلى اللَّهُ علیه وسلم فی مَرَضِهِ فَبَكَیْتِ ثُمَّ أَكْبَبْتُ علیه ثَانِیَةً فَضَحِكَتِ قالت أَكْبَبْتُ علیه فَأَخْبَرَنِی أَنَّهُ مَیِّتٌ فَبَكَیْتُ ثُمَّ أَكْبَبْتُ علیه فَأَخْبَرَنِی أَنِّی أَوَّلُ أَهْلِ بَیْتِهِ لُحُوقًا بِهِ وَأَنِّی سَیِّدَةُ نِسَاءِ أَهْلِ الْجَنَّةِ إِلا ما كان من مَرْیَمَ بنتِ عِمْرَانَ فَضَحِكَتُ.
Aeshe says '' I said to Fateme, the daughter of the messenger of God (peace of Allah be upon him and his descendants), '' you put your head on the body of your father and cried when your father was sick and repeated it once more and laughed. He said '' at the first time, he informed the news of his death; therefore, I cried. At the second time, he said '' you are the first person from my Ahle Beit(peace be upon them); if you join me, you will be the master of the women of the heaven.
Al-Tabarani, Soleiman Ben Ahmad Ben Ayub Abu Al-Ghasem (died in 360 Hejira), Al-Moajem Al-Kabir, v 22 p 419, Researched by: Hamdi Ben Abd Al-Majid Al-Salafi, Published by: Maktab Al-Zahra, Al-Movasel, Second Edition; 1404 Hejira- 1983
Conclusion
There is no contrast between the martyrdom of Hazrat Mohsen (peace be upon him) and the narration that the messenger of God (peace of Allah be upon him and his descendants) annunciated to Hazrat Zahra (peace be upon her) '' you are the first person from Ahle Beit that will join me'' because Ahle Beit is attributed to five persons in the opinion of the messenger of God (peace of Allah be upon him and his descendants) and Hazrat Mohsen (peace be upon him) is not one of five persons.