(36) باب خَوْفِ الْمُؤْمِنِ مِنْ أَنْ يَحْبَطَ عَمَلُهُ وَهُوَ لاَ يَشْعُرُ
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)."
Reference: Sahih al-Bukhari 49
In-book reference: Book 2, Hadith 42
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 1, Book 2, Hadith 47