It is narrated from Sayyiduna Muawiyah (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: "The eyes are the bond of the private parts; when the eyes sleep, the bond is loosened (and a person does not realize when wind passes from him)."
Hadith Referenceمسند احمد / مسند الشاميين / 16879
Hadith Gradingحکم دارالسلام:إسناده ضعيف لضعف أبى بكر