John Lightfoot on Matthew 5:28

[Whosoever looketh upon a woman to lust after her, &c.] "He that looketh upon a woman's heel, is as if he looked upon her belly: and he that looks upon her belly, is as if he lay with her." And yet, It was Rabban Gamaliel's custom to look upon women. And in the other Talmud; "He that looks upon the little finger of a woman, is as if he looked upon her privy parts." And yet "Rabh Gidal and R. Jochanan were wont to sit at the place of dipping, where the women were washed; and when they were admonished by some of the danger of lasciviousness, R. Jochanan answered, 'I am of the seed of Joseph, over whom an evil affection could not rule.'"