Messenger of Allah ﷺ used to practice Iʿtikaf in the last ten nights of Ramadan and used to say, "Look for the Night of Qadr in the last ten nights of the month of Ramadan."
كَانَ رَسُولُ اللَّهِ ﷺ يُجَاوِرُ فِي الْعَشْرِ الأَوَاخِرِ مِنْ رَمَضَانَ وَيَقُولُ تَحَرَّوْا لَيْلَةَ الْقَدْرِ فِي الْعَشْرِ الأَوَاخِرِ مِنْ رَمَضَانَ