Sahih al-Bukhari Book 33, Hadith 19
The Prophet (ﷺ) used to perform I`tikaf every year in the month of Ramadan for ten days, and when it was
the year of his death, he stayed in I`tikaf for twenty days.
that `Umar had vowed in the Pre-Islamic period to perform I`tikaf in Al-Masjid-al-Haram. (A subnarrator thinks that `Umar vowed to perform I`tikaf for one night.) Allah's Messenger (ﷺ) said to `Umar, "Fulfill your vow."
Allah's Messenger (ﷺ) mentioned that he would practice I`tikaf in the last ten days of Ramadan. `Aisha asked his permission to perform I`tikaf and he permitted her. Hafsa asked `Aisha to take his permission for her, and she did so. When Zainab bint Jahsh saw that, she ordered a tent to be pitched for her and it was pitched for her. Allah's Messenger (ﷺ) used to proceed to his tent after the prayer. So, he saw the tents ans asked, "What is this?" He was told that those were the tents of Aisha, Hafsa, and Zainab. Allah's Apostle said, "Is it righteousness which they intended by doing so? I am not going to perform I`tikaf." So he returned home. When the fasting month was over, he performed Itikar for ten days in the month of Shawwal.