Sahih Muslim
The Book of Fasting (Kitab Al-Sawm)
Book Number: 006 / Hadith Number: 2624
Abu Huraira (Allah be pleased with him) reported Allah's Messenger (may peace be upon him) as saying: I was shown Lailat-ul-Qadr; then some members of my family awoke me up, then I was caused to forget it. So seek it in the last week. Harmala said: (The Holy Prophet did not say:" I was made to forget," but he stated):" But I forgot it."