Mukhtasar Bukhari

Sayyiduna Ibn Abbas (may Allah be pleased with them both) in another narration says that the Messenger of Allah (peace and blessings of Allah be upon him) said: "Laylat al-Qadr is in the last ten nights; when nine nights have passed (i.e., the twenty-ninth) or when seven nights remain (i.e., the twenty-third)." By this, he (peace be upon him) meant Laylat al-Qadr.