But we do not call upon everyone to observe i'tikaf whenever he wishes. Rather, the best guidance is the guidance of Muhammad ﷺ. Had the Messenger ﷺ known that observing i'tikaf outside Ramadan—or even outside its final ten nights—entailed a sunnah and reward, he would have made it clear to the Ummah so that they might act upon it. For he was told: “O Messenger, convey that which has been revealed to you from your Lord. And if you do not, then you have not conveyed His message.” [al-Ma'idah: 67]
Consider the hadith of Abu Sa'id: the Messenger ﷺ observed i'tikaf during the first ten days, then the middle ten days; then he was told that Laylat al-Qadr was in the final ten nights, so he observed i'tikaf during the final ten days. (1) Yet in the following year, he did not observe i'tikaf during the first ten days or the middle ten days, despite the fact that these had previously been periods in which he observed i'tikaf, and despite Ramadan being the month of i'tikaf.
Accordingly, i'tikaf is not a sunnah in the sense that people are not to be urged to observe it except during the final ten nights. However, if someone voluntarily wishes to observe i'tikaf at another time, he is not to be forbidden from doing so, drawing support from the hadith of Umar, may Allah be pleased with him. Nor do we say that doing so is an innovation; rather, we say: It is better for you to follow the example of the Messenger ﷺ.
There are analogous cases to the hadith of Umar. One is the man who would lead his companions in prayer and conclude his recitation with Surat al-Ikhlas; the Messenger ﷺ did not censure him for this, (2) but he did not prescribe it