Let us see an authentic chain for this narration

قال أحمد ابن زهير حدثنا عبيد الله بن عمر القواريري حدثنا مؤمل بن إسماعيل حدثنا سفيان الثوري عن يحيى بن سعيد عن سعيد بن المسيب قال كان عمر يتعوذ بالله من معضلة ليس لها أبو الحسن وقال في المجنونة التي أمر برجمها وفى التي وضعت لستة أشهر فأراد عمر رجمها فقال له على إن الله تعالى يقول وحملة وفصاله ثلاثون شهرا الحديث وقال له إن الله رفع القلم عن المجنون الحديث فكان عمر يقول لولا على لهلك عمر

[Al Istiaab ibn abdul Bar, vol 3, page 1103]

“Umar used to ask God to keep him away from dilemmas that Abu Hassan (Amir al-Mu’minin Ali (as)) was not available to solve. Umar said
(the same phrase) about the insane woman who he had sentenced to be stoned (to death) and about the woman who gave birth after being pregnant for only six months and he decided to stone (to death). Ali (as) said to him, verily Allah has said ‘The carrying* of the [child] and his breast feeding was [a period of] thirty months (Quran 46:15)’**… He also said: ‘verily Allah has raised the pen^ off the insane ones’…so Umar said: ‘If Ali (as) had not been there, Umar would have been ruined.’”

*During pregnancy

**A child is usually born 9 months after intercourse. Since this particular child was born 6 months after intercourse, Umar
had thought the child was illegitimate and its mother had committed adultery 9 months earlier. To prove that a child can
be born only 6 months after intercourse, Amir al-Mu’minin (as) had recited this verse which speaks of a child whose
carrying and breastfeeding period was 30 months. According to the Quran 2:233 & 31:14, a woman breast feeds her child
for 2 complete years which equals to 24 months. 30 minus 24 equals 6 months which would be the time of carrying for that

^This means Allah does not record their sins and thus they have no responsibility.


1-Sa’eed b. Musayyib:

He is one of the narrators in Sahih Bukhari. Ibn Hajar says:

“Sa’eed Bin Musayyib is… One of the great, firm, and knowledgeable scholars and it is agreed that his narrations are among the best of
narrations, and Ibn al-Madini said: ‘I don’t know among the Tabe’in (scholars that lived after the time of the prophet) a man more
knowledgeable than him.’” 

Ibn Hajar al-Asqalani, Taqrib al-Tahdhib, vol. 1, p. 364

2-Yahya Bin Sa’eed:

He is one of the narrators in Sahih Bukhari. Al-Dhahabi says:

“Yahya b. Sa’eed b. Quays b. Amr, imam Abu-Sa’eed al-Ansari, Qadi al-Saffah. According to Anas, ibn al-Musayyib, Malik, and al-Qattan: ‘(He
was) a memorizer (of hadith), knowledgeable, and a proof (to the people)’ he died in 143 H.” 

Al-Dhahabi, al-Kashif Fi Ma’rifat Man Lahu Riwayat Fi Kutub al-Sitta, vol. 2, p. 366

Ibn Hajar says:

“Yahya b. Sa’eed b. Qays al-Ansari al-Madani, Abu-Sa’eed al-Qadi is a proven trustworthy (person).” 

Ibn Hajar, Taqrir al-Tahdhib, vol. 2, p. 303

3-Sufyan al-Thawri:

He is one of the narrators in Sahih Bukhari. Al-Mizzi says:

“Shu’ba, Sufyan b. Uyayna, Abu-Asim al-Nabil, Yahya b. Mu’een, along with other scholars have said: ‘Sufyan is the ‘leader of believers’ in (the
science of) narrations.’”

Tahdhib al-Kamal, al-Mazi, vol. 11, p. 165

4-Muammil b. Isma’il: 

Al-Dhahabi says:

“Muammil b. Ismail al-Basri al-Umari their leader… Abu-Hatam said: Strongly truthful in traditions (sunna), made many mistakes… died 206

Al-Dhahabi, al-Kashif Fi Ma’rifat Man Lahu Riwayat Fi Kutub al-Sitta, vol. 2, p. 309

Ibn Hajar says:

“Ibn Abi Khaithama said according to Ibn Mu’een ‘He is trustworthy (thiqa)’, and Uthman al-Daremi said: I said to Ibn Mu’een: ‘what is his
status?’ he said ‘A trustworthy (person) (thiqa)’, I said: ‘do you prefer him to Ubaid Allah?’ meaning Ibn Musa, and he didn’t prefer (one to the other), and Abu-Hatam said: ‘Strongly truthful in traditions (sunna), made many mistakes.’” 

Ibn Hajar, Tahdhib al-Tahdhib, vol. 10, p. 340

Although Muammil b. Ismail is trustworthy (thiqa) and strongly truthful, some might argue that he has made mistakes and this narration could be one of his mistakes. Our answer is that one must first prove that the current narration is one of his mistakes before putting forward this claim. Furthermore the current narration is mutawatir and has been narrated many times by numerous people. Considering this fact there remains no doubt that no mistake has been made by the narrator in transmitting this particular narration.

5-Abdullah b. Umar al-Qawariry:

He is one of the narrators in Sahih Bukhari. Al-Dhahabi says:

“Ubaid Allah b. Umar al-Qawariry Abu Sa’eed al-Basri, the great memorizer (hafiz), narrated one hundred thousand narrations… died in
the month of Dhil Hijja, 235 H.”

Al-Dhahabi, al-Kashif Fi Ma’rifat Man Lahu Riwayat Fi Kutub al-Sitta, vol. 1, p. 685

Ibn Hajar says:

“Ubaid Allah b. Umar b. Maysara al-Qawariry Abu-Sa’eed … is a proven trustworthy (person) (thiqa).” 

Ibn Hajar, Taqrib al-Tahdhib, vol. 1, p. 637

6-Ahmed b. Zuhair:

Ibn Hajar says:

“Ahmed b. Zuhair b. Harb b. Shaddad…A Great Memorizer (hafiz) son of a memorizer (hafiz)… Al-Khatib said: ‘He was trustworthy (thiqa), very
knowledgeable, skilled, a memorizer (hafiz), well aware about the times of the people and the leaders (imams) of literature.”

Ibn Hajar, Lisan al-Mizan, vol. 1, p. 174

Therefore, based on Sunni sources this hadith is authentic.

This article is basically taken from the Persian article 
and you can download this article in English language in pdf format here