Musnad Ahmad 1007:46

Yahya ibn Ishaq narrated to us, Ibn Lahi'ah informed us, from Ubayd Allah ibn Abi Ja'far, from Ibn Abi Qatadah, from his father, who said: 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, a serpent will be sent to him on the Day of Resurrection."