Language:
كتاب الإيمان
2  
Belief
(36)
Chapter: (What is said regarding) the fear of a believer that his good deeds may be annulled (lost) without his knowledge
(36)
باب خَوْفِ الْمُؤْمِنِ مِنْ أَنْ يَحْبَطَ عَمَلُهُ وَهُوَ لاَ يَشْعُرُ
Sahih al-Bukhari 49

Narrated 'Ubada bin As-Samit:

"Allah's Messenger (ﷺ) went out to inform the people about the (date of the) night of decree (Al-Qadr) but there happened a quarrel between two Muslim men. The Prophet (ﷺ) said, "I came out to inform you about (the date of) the night of Al-Qadr, but as so and so and so and so quarrelled, its knowledge was taken away (I forgot it) and maybe it was better for you. Now look for it in the 7th, the 9th and the 5th (of the last 10 nights of the month of Ramadan)."

أَخْبَرَنَا قُتَيْبَةُ بْنُ سَعِيدٍ، حَدَّثَنَا إِسْمَاعِيلُ بْنُ جَعْفَرٍ، عَنْ حُمَيْدٍ، عَنْ أَنَسٍ، قَالَ أَخْبَرَنِي عُبَادَةُ بْنُ الصَّامِتِ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم خَرَجَ يُخْبِرُ بِلَيْلَةِ الْقَدْرِ، فَتَلاَحَى رَجُلاَنِ مِنَ الْمُسْلِمِينَ فَقَالَ ‏ "‏ إِنِّي خَرَجْتُ لأُخْبِرَكُمْ بِلَيْلَةِ الْقَدْرِ، وَإِنَّهُ تَلاَحَى فُلاَنٌ وَفُلاَنٌ فَرُفِعَتْ وَعَسَى أَنْ يَكُونَ خَيْرًا لَكُمُ الْتَمِسُوهَا فِي السَّبْعِ وَالتِّسْعِ وَالْخَمْسِ ‏"‏‏.‏
Reference : Sahih al-Bukhari 49
In-book reference : Book 2, Hadith 42
USC-MSA web (English) reference : Vol. 1, Book 2, Hadith 47
  (deprecated numbering scheme)