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.
Sunan an-Nasa'i Book 35, Hadith 60
← Previous Hadith "Sa'd bin 'Ubadah came to the Prophet and said: 'My mother died and she had sworn a vow, but she did not fulfill it.' He said: 'Fulfill it on her behalf.'"

Sunan an-Nasa'i Book 35, Hadith 59 Next Hadith → "Umar had made a vow to spend a night in 'Itikaf in Al-Masjid Al-Haram. He asked the Messenger of Allah about that, and he ordered him to perform the 'Itikaf."

Sunan an-Nasa'i Book 35, Hadith 61