Sunan Ibn Majah
1773
Sahih+2

It was narrated from ‘Abdullah bin ‘Umar that:The Messenger of Allah (ﷺ) used to spend the last ten days of Ramadan in I’tikaf. Nafi' said: " Abdullah bin 'Umar showed me the place where the Messenger of Allah (ﷺ) used to observe I'tikaf

SahihAl-Albani
SahihMuhammad Fouad Abd al-Baqi