From Sahih Bukhari (Hadith 2034):
Narrated `Aisha:The Prophet (ﷺ) intended to practice I`tikaf and when he reached the place where he intended to perform I`tikaf, he saw some tents, the tents of `Aisha, Hafsa and Zainab. So, he said, "Do you consider that they intended to do righteousness by doing this?" And then he went away and did not perform I`tikaf (in Ramadan) but performed it in the month of Shawwal for ten days
Reference: Bukhari 2034