Musannaf Ibn Abi Shayba 9:1491

Abu Mu'awiyah narrated to us, from Hajjaj, from Muhammad ibn Sulayman ibn Abi Hathma, from his uncle Sahl ibn Abi Hathma, who said: I saw Muhammad ibn Maslamah following Thubaytah bint al-Dahhak with his gaze while she was on one of the paths of Medina. I said, "Do you do this?" He said, "Yes, I heard the Messenger of Allah, may Allah bless him and grant him peace, say: 'If Allah casts into the heart of a man the proposal of a woman, there is no harm in him looking at her.'"