Allah's Messenger (ﷺ) used to practice I`tikaf in the last ten days of the month of Ramadan.
Sahih al-Bukhari Book 33, Hadith 1
← Previous Hadith 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.

Sahih al-Bukhari Book 32, Hadith 11 Next Hadith → (the wife of the Prophet) The Prophet (ﷺ) used to practice I`tikaf in the last ten days of Ramadan till he died and then his wives used to practice I`tikaf after him.

Sahih al-Bukhari Book 33, Hadith 2