Sayyiduna Sahl bin Abi Hathmah (may Allah be pleased with him) said: Some people of the Ansar passed by Sayyiduna Muhammad bin Maslamah (may Allah be pleased with him) while he was peeping at a girl of Banu al-Najjar, and they said: Subhan Allah (Glory be to Allah)! If one of our young men had done this, we would have considered it shameful. He (that is, Muhammad bin Maslamah (may Allah be pleased with him)) said: I heard the Messenger of Allah (peace and blessings be upon him) say: "When Allah puts into a man's heart (the thought of) proposing marriage to a woman, there is no harm in his looking at her." Yahya bin al-Ala' narrated it thus from al-Hajjaj, from Muhammad bin Uthman.
Hadith Referenceالمعجم الكبير للطبراني / باب الميم / 16548