It is narrated from Sayyiduna Abdullah bin Unays (may Allah be pleased with him) that he asked the Messenger of Allah (peace and blessings be upon him) about Laylat al-Qadr, and he (peace and blessings be upon him) said: "I was shown it, then I was made to forget it; seek it in the latter half." Then he asked him again, and he (peace and blessings be upon him) said: "When twenty-three nights of the month have passed."
Abd al-Aziz said: My mother told me that Sayyiduna Abdullah bin Unays (may Allah be pleased with him) used to spend the nights in worship from the sixteenth night until the twenty-third night.
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 13944