Musnad Ahmad 27:100

Sufyan narrated to us, from al-Zuhri, from Salim, from his father: A man saw that Laylat al-Qadr was the night of the twenty-seventh, or such and such. The Messenger of Allah (peace and blessings of Allah be upon him) said: "I see that your visions have coincided, so seek it in the remaining ten [nights], in the odd-numbered ones among them."