Sayyiduna Ibn Umar (may Allah be pleased with them both) narrates that when we returned from Hunayn, Umar (may Allah be pleased with him) asked the Noble Prophet (peace and blessings be upon him) about the vow he had made in the days of ignorance, that is, the vow of i'tikaf (seclusion in the mosque) for one day. So the Noble Prophet (peace and blessings be upon him) instructed him to fulfill it.