O Nārada, the evacuating outlet of the universal form of the Lord is the abode of the controlling deity of death, Mitra, and the evacuating hole and the rectum of the Lord is the place of envy, misfortune, death, hell, etc.
Srimad Bhagavata Purana
श्रीमद्भागवतमहापुराणम्
मूल श्लोकः
पराभूतेरधर्मस्य तमसश्चापि पश्चिमः । नाड्यो नदनदीनां तु गोत्राणामस्थिसंहतिः
parābhūteradharmasya tamasaścāpi paścimaḥ | nāḍyo nadanadīnāṃ tu gotrāṇāmasthisaṃhatiḥ
SB 2.6.9