Sunan an Nasai
3820
Sahih+2

It was narrated from Ibn 'Umar, that 'Umar had vowed to spend a night in 'Itikaf during the Jahiliyyah. He asked the Messenger of Allah about that, and he ordered him to perform the 'Itikaf

SahihAbu Ghuddah
SahihAl-Albani