Nahj al-Balāgha

١٧. وَسُئِلَ (عليه ‏السلام) عَنْ قَوْلِ الرَّسُولِ (صلى‌ الله‌ عليه‌ وآله‌ وسلم): غَيِّرُوا الشَّيْبَ وَلَا تَشَبَّهُوا بِالْيَهُودِ. فَقَالَ (عليه ‏السلام):

17. Amīr al-mu’minīn, peace be upon him, was asked to explain the saying of the Messenger of Allāh: “Banish your old age (by hair-dye) and do not acquire resemblance to the Jews.” Amīr al-mu’minīn replied:

إِنَّمَا قَالَ (صلى‌ الله‌ عليه‌ وآله‌ وسلم) ذَلِكَ وَالدِّينُ قُلٌّ فَأَمَّا الْآنَ وَقَدِ اتَّسَعَ نِطَاقُهُ وَضَرَبَ بِجِرَانِهِ فَامْرُؤٌ وَمَا اخْتَارَ.

The Prophet (S) said this at a time when the religion was confined to a few, but now that its expanse has widened and it is firmly settled everyone is free in his action. [1]