It is narrated from Sayyiduna Umar (may Allah be pleased with him) that he 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: "Yes! Let him perform ablution as for prayer and then sleep."
Hadith Referenceمسند احمد / مسند الخلفاء الراشدين / 235
Hadith Gradingحکم دارالسلام:صحيح لغيره، عبد الله ابن عمر العمري شيخ عبدالرزاق - وإن كان ضعيفا - توبع