(69) باب هَلْ يَأْخُذُ الإِمَامُ إِذَا شَكَّ بِقَوْلِ النَّاسِ
Narrated Abu Huraira:
Once Allah's Messenger (ﷺ) prayed two rak`at (instead of four) and finished his prayer. Dhul-Yadain asked him whether the prayer had been reduced or whether he had forgotten. Allah's Messenger (ﷺ) asked the people whether Dhul-Yadain was telling the truth. The people replied in the affirmative. Then Allah's Apostle stood up, offered the remaining two rak`at and then finished his prayer with Taslim and then said, "Allahu Akbar." He followed it with two prostrations like ordinary prostrations or a bit longer.
Reference: Sahih al-Bukhari 714
In-book reference: Book 10, Hadith 109
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 1, Book 11, Hadith 682