Once, Sayyiduna Umar (may Allah be pleased with him) asked the Prophet (peace and blessings be upon him), "If a person becomes impure by choice, can he sleep in that state?" The Prophet (peace and blessings be upon him) said: "If he wishes, he may perform ablution and then sleep (and if he wishes, he may sleep as he is)."
Hadith Referenceمسند احمد / مسند الخلفاء الراشدين / 165