مِشْكَاةُ الْمَصَابِيحِ
Mishkat al-Masabih 3125
Marriage
Looking at a Woman who is asked in Marriage, and an Explanation of what may not be seen - Section 3
وَعَنِ الْحَسَنِ مُرْسَلًا قَالَ: بَلَغَنِي أَنَّ رَسُولَ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ قَالَ: «لَعَنَ اللَّهُ النَّاظِرَ وَالْمَنْظُورَ إِلَيْهِ» . رَوَاهُ الْبَيْهَقِيُّ فِي شُعَبِ الْإِيمَانِ
Al-Hasan told in mursal form that he heard God’s Messenger had said, “God curse the one who looks and the one who is looked at!” Baihaqi transmitted it in Shu'ab al-iman.
Mishkat al-Masabih, 3125ضَعِيف (الألباني)