It is narrated from Sayyiduna Ibn Umar (may Allah be pleased with them both) that once Sayyiduna Umar (may Allah be pleased with him) asked the Prophet (peace and blessings be upon him) that sometimes during the night, ghusl becomes obligatory upon him. The Prophet (peace and blessings be upon him) said to him: Perform wudu, wash your private parts, and then go to sleep.