Sahih al-Bukhari Book 32, Hadith 10
The Prophet (ﷺ) came out to inform us about the Night of Qadr but two Muslims were quarreling with
each other. So, the Prophet (ﷺ) said, "I came out to inform you about the Night of Qadr but such-and-such
persons were quarreling, so the news about it had been taken away; yet that might be for your own
good, so search for it on the 29th, 27th and 25th (of Ramadan).
Allah's Messenger (ﷺ) said, "The Night of Qadr is in the last ten nights of the month (Ramadan), either on the first nine or in the last (remaining) seven nights (of Ramadan)." Ibn `Abbas added, "Search for it on the twenty-fourth (of Ramadan).
With the start of the last ten days of Ramadan, the Prophet (ﷺ) used to tighten his waist belt (i.e. work hard) and used to pray all the night, and used to keep his family awake for the prayers.