Sahih Muslim
The Book of Fasting (Kitab Al-Sawm)
Book Number: 006 / Hadith Number: 2617
Ibn 'Umar (Allah be pleased with them) reported that some persons among the Companions of the Apostle of Allah (may peace be upon him) were shown Lailat- ul-Qadr while sleeping in the last week (of Ramadan). Thereupon Allah's Messenger (may peace be upon him) said: I see that your dreams agree regarding the last week; so he who wants to seek it should seek it in the last week (during the night).