The Prophet ﷺ was asked about Laylat al-Qadr, and he said, "I had been informed of it, but then it slipped from me. So seek it in the last seven nights, or the last three nights."
سئل النبي ﷺ عن ليلة القدر، فقال: كنت أعلمتها، ثم انفلت مني، فاطلبوها في سبع يبقين، أو ثلاث يبقين.
Bazzar narrated it - Kashf Astar (1028) - from Yusuf bin Musa, who said, Abdullah bin Jahm narrated to us, who said, Amr bin Abu Qays narrated to us, from Zubayr bin Adi, from Abu Waail, from Abdullah, and he related it.Its isnad is hasan because of Abdullah bin Jahm Razi, for his hadith is hasan. Abu Zura said, "He is truthful." Ibn Hibban mentioned him in Thiqat, except that Abu Hatim did not record hadith from him, though he had seen him, and he held Shia leanings. The rest of the narrators are trustworthy.His wording, "seven remaining," is as it appears in Kashf Astar, and likewise in Majma al-Zawaid by Haythami, while in Bahr Zakhkhar it appears as "nine remaining," which is a distortion. The correct version, as I have said, is "seven remaining."As for the narrator's statement, "or three remaining," expressed with uncertainty, it is in fact certain, as comes in Sahih Muslim.