Ali bin Husayn (may Allah have mercy on him) narrates from his father, Sayyiduna Husayn bin Ali (may Allah be pleased with him), that the Messenger of Allah (peace and blessings be upon him) said: "Spiritual retreat (i'tikaf) for ten days in Ramadan is equal to two Hajjs and two Umrahs."
Hadith Referenceالمعجم الكبير للطبراني / باب الحاء / 2875