It is narrated from Hazrat Aisha (may Allah be pleased with her) that the Prophet (peace and blessings be upon him) used to observe i'tikaf during the last ten days of Ramadan until Allah called him to Himself.
Hadith Referenceمسند احمد / مسند النساء / 25358
Hadith Gradingحکم دارالسلام:حديث صحيح، وهذا إسناد مختلف فيه، خ: 2026، م: 1172