Sahih al-Bukhari Book 33, Hadith 15
We practiced I`tikaf with Allah's Messenger (ﷺ) in the middle ten days (of Ramadan). In the morning of the
twentieth (of Ramadan) we shifted our baggage, but Allah's Messenger (ﷺ) came to us and said, "Whoever
was m I`tikaf should return to his place of I`tikaf, for I saw (i.e. was informed about the date of) this
Night (of Qadr) and saw myself prostrating in mud and water." When I returned to my place the sky
was overcast with clouds and it rained. By Him Who sent Muhammad with the Truth, the sky was
covered with clouds from the end of that day, and the mosque which was roofed with leafstalks of
date palm trees (leaked with rain) and I saw the trace of mud and water over the nose of the Prophet (ﷺ)
and its tip.
Safiya went to the Prophet (ﷺ) while he was in I`tikaf. When she returned, the Prophet (ﷺ) accompanied her walking. An Ansari man saw him. When the Prophet (ﷺ) noticed him, he called him and said, "Come here. She is Safiya. (Sufyan a sub-narrator perhaps said that the Prophet (ﷺ) had said, "This is Safiya"). And Satan circulates in the body of Adam's offspring as his blood circulates in it." (A sub-narrator asked Sufyan, "Did Safiya visit him at night?" He said, "Of course, at night.")
Allah's Messenger (ﷺ) used to practice I`tikaf every year in the month of Ramadan. And after offering the morning prayer, he used to enter the place of his I`tikaf. `Aisha asked his permission to let her practice I`tikaf and he allowed her, and so she pitched a tent in the mosque. When Hafsa heard of that, she also pitched a tent (for herself), and when Zainab heard of that, she too pitched another tent. When, in the morning, Allah's Messenger (ﷺ) had finished the morning prayer, he saw four tents and asked, "What is this?" He was informed about it. He then said, "What made them do this? Is it righteousness? Remove the tents, for I do not want to see them." So, the tents were removed. The Prophet (ﷺ) did not perform I`tikaf that year in the month of Ramadan, but did it in the last ten days of Shawwal.