(15) بَابُ إِذَا حَنِثَ نَاسِيًا فِي الأَيْمَانِ
Narrated `Abdullah bin `Amr bin Al-As:
While the Prophet (ﷺ) was delivering a sermon on the Day of Nahr (i.e., 10th Dhul-Hijja-Day of slaughtering the sacrifice), a man got up saying, "I thought, O Allah's Messenger (ﷺ), such-and-such a thing was to be done before such-and-such a thing." Another man got up, saying, "O Allah's Messenger (ﷺ)! As regards these three (acts of Hajj), thought so-and-so." The Prophet (ﷺ) said, "Do, and there is no harm," concerning all those matters on that day. And so, on that day, whatever question he was asked, he said, "Do it, do it, and there is no harm therein."
Reference: Sahih al-Bukhari 6665
In-book reference: Book 83, Hadith 43
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 8, Book 78, Hadith 658