Musnad Ahmad 1153:432

Sulayman narrated to us, he said: Isma'il informed us, he said: Abu Suhayl informed me, from his father, from 'Aishah, that the Prophet, peace and blessings of Allah be upon him, said: "Seek the Night of Decree (Laylat al-Qadr) in the odd-numbered nights of the ten (final nights of Ramadan)."