ʿUyūn akhbār al-Riḍā

131 - وَبِهذَا الإِسنادِ عَنْ عَلِىِّ بْنِ أَبِي طالِبٍ‏ عَلَيْهِالسَّلامُ قالَ: كانَ النَّبِيُ‏ صَلَّى اللهُ عَلَيْهِ وَآلِهِ لا يَأْكُلُ الكُلّيَتَيْنِ مِن غَيْرِ أَن يُحَرِمَّهُما لِقُربِهِما مِن البُوْلِ.

31-131 According to the same documentation, Ali ibn Abi Talib (a.s.) said, “The Prophet (S) never forbade eating kidneys, but he (a.s.) wouldn’t eat them. The Prophet (S) said it was because they produce urine.”