Among the most authentic hadiths on this subject is Ibn Mas'ūd’s hadith concerning the exercise of judgment, recorded by both al-Bukhārī and Muslim in their Sahīh collections. The hadith of Abū Sa'īd was recorded by Muslim alone, but the hadith of 'Abd al-Rahmān ibn 'Awf corroborates it. Together, the two are comparable to Ibn Mas'ūd’s hadith, recorded in the two Sahīh collections through Ibrāhīm, from 'Alqamah, from 'Abd Allāh ibn Mas'ūd, who said:

“The Messenger of Allah, may Allah bless him and grant him peace, prayed—Ibrāhīm said: ‘He prayed either more or fewer units.’ When he gave the concluding salutation, he was asked: ‘O Messenger of Allah, has something changed concerning the prayer?’ He asked: ‘What do you mean?’ They said: ‘You prayed such-and-such a number of units.’ He then folded his legs, faced the direction of prayer, performed two prostrations, and gave the concluding salutation. He then turned to face us and said: ‘Had anything changed concerning the prayer, I would have informed you. But I am only human: I forget just as you forget. So when I forget, remind me. If any of you has doubts during his prayer, let him exercise his judgment to determine what is correct, complete his prayer on that basis, and then perform two prostrations.’”

In one of al-Bukhārī’s chains of transmission, the wording is:

“He was asked: ‘O Messenger of Allah, has the prayer been shortened, or did you forget?’ He asked: ‘What do you mean?’ They said: ‘You prayed such-and-such a number of units.’ He then led them in two prostrations and said: ‘These two prostrations are for someone who does not know whether he has prayed too many units or too few. He should exercise his judgment to determine what is correct, complete his prayer on that basis, and then perform two prostrations.’”

Another version recorded by al-Bukhārī reads:

“Let him complete his prayer on that basis, then give the concluding salutation, and then perform two prostrations.”

A version recorded by Muslim reads:

“Let him consider which possibility is more likely to be correct.”

Another version he records reads:

“Let him exercise his judgment to determine what he believes to be correct.”

Another version reads:

“Let him exercise his judgment to determine which possibility is closest to being correct.”