Sahih al-Bukhari 5898

Arabic

وَقَالَ لَنَا أَبُو نُعَيْمٍ حَدَّثَنَا نُصَيْرُ بْنُ أَبِي الأَشْعَثِ، عَنِ ابْنِ مَوْهَبٍ، أَنَّ أُمَّ سَلَمَةَ، أَرَتْهُ شَعَرَ النَّبِيِّ صلى الله عليه وسلم أَحْمَرَ‏.‏

English translation

Ibn Mauhab also said that Um Salama had shown him the red hair of the Prophet

Reference: Sahih al-Bukhari 5898, Book of Dress. English translation by Dr. Muhammad Muhsin Khan.