Sayyiduna Anas bin Malik (may Allah be pleased with him) narrates that when the Noble Prophet (peace and blessings be upon him) was residing, he would observe i'tikaf during the last ten days of Ramadan, but if he traveled during this period, then the following year he would observe i'tikaf for twenty days.
Hadith Referenceالفتح الربانی / كتاب الصيام / 3998
Hadith Gradingمحدثین:صحیح
Hadith Takhrij«اسناده صحيح علي شرط الشيخين۔ اخرجه الترمذي: 803، (انظر مسند أحمد ترقيم الرسالة: 12017 ترقیم بيت الأفكار الدولية: 12040»
Brief Explanation
Benefits: … It is understood from this that if, due to some excuse, i‘tikaf (spiritual retreat) is missed, then it can be made up (qada) in the next Ramadan or in any other month before that.