Musnad Ahmad 1007:41

Abu Sa'id, the freed slave of Banu Hashim, narrated to us, Ibn Lahi'ah narrated to us, 'Ubayd Allah ibn Abi Ja'far narrated to us, from Ibn Abi Qatadah, from his father, that the Messenger of Allah (peace and blessings of Allah be upon him) said: "Whoever sits on the bed of a woman whose husband is absent, Allah will appoint for him on the Day of Resurrection a serpent."