It wasnarrated from 'Abdullah bin 'Umar that:
The Messenger of Allah(ﷺ) used to spend the last ten days of Ramadan in I'tikaf. (RU)
English reference (RU): Vol. 1, Book 7, Hadith 1773 (RU)
Arabic reference (RU): Book 7, Hadith 1845 (RU)