Musnad Abi Ya'la 3712 — a man from the tribe of Juhaynah said: O

It is narrated from Sayyiduna Anas bin Malik (may Allah be pleased with him) that a man from the tribe of Juhaynah said: "O Messenger of Allah (peace and blessings be upon him), we live (far from the town) in a place, as you know, and we are not able to be present for the whole month, so tell us about Laylat al-Qadr." He (peace and blessings be upon him) said: "Be present for the last seven nights of the month." He said that he was not able to do even that, so he (peace and blessings be upon him) said: "Then seek it on the night when seven nights remain, and it is this very night." He said: "O Messenger of Allah (peace and blessings be upon him), this is the twenty-third night, and (counting thirty) eight nights remain?" So he (peace and blessings be upon him) said: "This month falls short in this way (that is, sometimes it has twenty-nine days), and (by that count) only seven nights now remain."