The Prophet ﷺ was asked about Laylat al-Qadr and said, "I had been informed of it, then it slipped from my memory. Seek it in the last seven nights, or in the last three nights."
سئل النبي ﷺ عن ليلة القدر، فقال: كنت أعلمتها، ثم انفلتت مني، فاطلبوها في سبع يبقين، أو ثلاث يبقين.
Bazzar narrated it in Kashf Astar (1028), from Abdullah bin Yusuf, who said, "Abdullah bin Jahm narrated to us, Amr bin Abu Qays narrated to us, from Zubayr bin Adi, from Abu Waail, from Abdullah," and he mentioned it. Its isnad is hasan because of Abdullah bin Jahm and his teacher Amr bin Abu Qays, for both of them are truthful. Haythami mentioned it in al-Majmu (3/176) and said, "Its narrators are trustworthy."