Musnad Ahmad 652:99

Muhammad ibn Ja'far and Abdullah ibn Bakr narrated to us, they said: Sa'id narrated to us, from Qatadah, from Habib ibn Salim—Ibn Bakr said: the freed slave of an-Nu'man ibn Bashir—from an-Nu'man ibn Bashir, that a man was brought to him who had had intercourse with his wife's slave girl. He said: "I will surely judge regarding him with the judgment of the Messenger of Allah (may Allah bless him and grant him peace): If she had made her lawful for you, I will give you one hundred lashes; and if she had not made her lawful for you, I will stone you." He said: So he found that she had indeed made her lawful for him, so he gave him one hundred lashes.