Sahih Muslim 2102
Sahih Muslim · Book 37: The Book of Clothes and Adornment · It Is Recommended To Dye White Hair With Yellow Or Red Dye, But Black Dye Is Haram
Jabir b. 'Abdullah reported that Abu Qubafa was led (to the andience of the Holy Prophet) on the day of the Conquest of Mecca and his head and beard were white like hyssop, whereupon Allah's Messenger (ﷺ) said:
وَحَدَّثَنِي أَبُو الطَّاهِرِ ، أَخْبَرَنَا عَبْدُ اللَّهِ بْنُ وَهْبٍ ، عَنِ ابْنِ جُرَيْجٍ ، عَنْ أَبِي الزُّبَيْرِ ، عَنْ جَابِرِ بْنِ عَبْدِ اللَّهِ ، قَالَ أُتِيَ بِأَبِي قُحَافَةَ يَوْمَ فَتْحِ مَكَّةَ وَرَأْسُهُ وَلِحْيَتُهُ كَالثَّغَامَةِ بَيَاضًا فَقَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " غَيِّرُوا هَذَا بِشَىْءٍ وَاجْتَنِبُوا السَّوَادَ " .
Change it with something but avoid black.