Musnad Ahmad 1061:5

Hassan ibn Musa narrated to us, Zuhayr narrated to us, from Abdullah ibn Isa, from Musa ibn Abdullah, from Abu Humayd, or Humaydah—the doubt is from Zuhayr—who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "If one of you proposes to a woman, there is no blame upon him to look at her if he is only looking at her for the sake of the proposal, even if she does not know."