ʿUyūn akhbār al-Riḍā
Hadith 237237 - وَبِإِسْنادِهِ قالَ: قالَ النَّبِي صَلَّى اللهُ عَلَيْهِوَآلِهِ: لا يَرى عَوْرَتِي غَيْرِ عَلِيِّ إِلاّ كافِرٌ.
31-237 According to the same documentation, the Prophet (S) said, “Should anyone but Ali (a.s.) look at my private parts he would be an atheist.”