Sahih Bukhari Volume 5, Book 59, Hadith Number 746.

Narrated By Ibn Abu Habib : Abu Al-Khair said, “As-Sanabih, I asked (me), ‘When did you migrate?’ I (i.e. Abu Al-Khair) said, ‘We went out from Yemen as emigrants and arrived at Al-Juhfa, and there came a rider whom I asked about the news. The rider said: We buried the Prophet five days ago.” I asked (As-Sanabihi), ‘Did you hear anything about the night of Qadr?’ He replied, ‘Bilal, the Mu’adhdhin of the Prophet informed me that it is on one of the seven nights of the last ten days (of Ramadan).”