Ibn `Umar (May Allah be pleased with them) reported:
The Messenger of Allah (ﷺ) used to observe I`tikaf in the last ten days of Ramadan.[Al-Bukhari and Muslim]. (RU)
App reference (RU): Book 10, Hadith 1 (RU)
Arabic/English book reference (RU): Book 10, Hadith 1268 (RU)