Musannaf Ibn Abi Shayba 33:771

Ibn ‘Uyaynah narrated to us, from ‘Amr, from ‘Ubayd ibn ‘Umayr, who said: From the sincerity of faith and its righteousness is performing ablution thoroughly despite difficulties. And from the sincerity of faith and its righteousness is that a man be alone with a beautiful woman, then he leaves her; he does not leave her except for the sake of Allah.