It is narrated from Sayyiduna Abu Umamah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "No Muslim casts an involuntary first glance at a woman and then lowers his gaze, except that Allah creates for him an act of worship whose sweetness he will feel."
Hadith Referenceالمعجم الكبير للطبراني / باب الصاد / 7811