Sunan Ibn Majah 1766

It was narrated that Abu Sa’eed Al-Khudri said:“We observed I’tikaf with the Messenger of Allah (ﷺ) during the middle ten days of Ramadan. He said: ‘I have been shown Lailatul-Qadr, then I was caused to forget it, so seek it in the last ten night, on the odd-numbered nights.’”