Sahih Bukhari

Narrated Ibn `Umar:`Umar said ""O Allah's Messenger (ﷺ)! I vowed to perform I`tikaf for one night in Al-Masjid-al-Haram, during the Pre-Islamic Period of ignorance (before embracing Islam). ""The Prophet (ﷺ) said, ""Fulfill your vow."" Ibn `Umar said to the lady, ""Pray on her behalf."" Ibn `Abbas said the same