Silsilat al-Ahadith al-Sahihah

It is narrated from Sayyiduna Ali (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "Seek the Night of Qadr in the last ten nights of (the month of) Ramadan, and if you are unable to do so, then (let it not happen that) you are overpowered regarding the last seven nights as well."