Sahih al-Bukhari, Book 77, Hadith 115 (In-Book) ⓘ
Ibn Mauhab also said that Um Salama had shown him the red hair of the Prophet.
وَقَالَ لَنَا أَبُو نُعَيْمٍ حَدَّثَنَا نُصَيْرُ بْنُ أَبِي الأَشْعَثِ، عَنِ ابْنِ مَوْهَبٍ، أَنَّ أُمَّ سَلَمَةَ، أَرَتْهُ شَعَرَ النَّبِيِّ صلى الله عليه وسلم أَحْمَرَ.
also referenced under: Hadith 5898 (DarusSalam) & Volume 7, Book 72, Hadith 785 (USC-MSA)