Language:
كتاب الأيمان والنذور
83
Oaths and Vows
(15)
Chapter: If someone does something against his oath due to forgetfulness
(15)
بَابُ إِذَا حَنِثَ نَاسِيًا فِي الأَيْمَانِ
Sahih al-Bukhari 6665

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."

حَدَّثَنَا عُثْمَانُ بْنُ الْهَيْثَمِ، أَوْ مُحَمَّدٌ عَنْهُ عَنِ ابْنِ جُرَيْجٍ، قَالَ سَمِعْتُ ابْنَ شِهَابٍ، يَقُولُ حَدَّثَنِي عِيسَى بْنُ طَلْحَةَ، أَنَّ عَبْدَ اللَّهِ بْنَ عَمْرِو بْنِ الْعَاصِ، حَدَّثَهُ أَنَّ النَّبِيَّ صلى الله عليه وسلم بَيْنَمَا هُوَ يَخْطُبُ يَوْمَ النَّحْرِ إِذْ قَامَ إِلَيْهِ رَجُلٌ فَقَالَ كُنْتُ أَحْسِبُ يَا رَسُولَ اللَّهِ كَذَا وَكَذَا قَبْلَ كَذَا وَكَذَا‏.‏ ثُمَّ قَامَ آخَرُ فَقَالَ يَا رَسُولَ اللَّهِ كُنْتُ أَحْسِبُ كَذَا وَكَذَا لِهَؤُلاَءِ الثَّلاَثِ‏.‏ فَقَالَ النَّبِيُّ صلى الله عليه وسلم ‏"‏ افْعَلْ وَلاَ حَرَجَ ‏"‏ لَهُنَّ كُلِّهِنَّ يَوْمَئِذٍ، فَمَا سُئِلَ يَوْمَئِذٍ عَنْ شَىْءٍ إِلاَّ قَالَ ‏"‏ افْعَلْ وَلاَ حَرَجَ ‏"‏‏.‏
Reference : Sahih al-Bukhari 6665
In-book reference : Book 83, Hadith 43
USC-MSA web (English) reference : Vol. 8, Book 78, Hadith 658
  (deprecated numbering scheme)