Sayyiduna Muhammad bin Maslamah (may Allah be pleased with him) said: I proposed marriage to a woman, and I began hiding (to see) her until I saw her. It was said to him: Do you do this, when you are a Companion of the Messenger of Allah (peace and blessings be upon him)? He said: I heard the Messenger of Allah (peace and blessings be upon him) say: "When Allah puts into the heart of any of you (the thought of) proposing marriage to a woman, there is no harm in his looking at her." Hafs bin Ghiyath narrated it thus, and Yazid bin Harun corroborated him.
Hadith Referenceالمعجم الكبير للطبراني / باب الميم / 16549