It is narrated from Sayyiduna Abu Umamah (may Allah be pleased with him) that he heard the Prophet (peace and blessings be upon him) say: "Whoever has a hair turn white in the path of Allah, it will be a light for him on the Day of Resurrection. And whoever shoots an arrow in the path of Allah, whether it misses or hits, will receive a reward equal to freeing a slave from the descendants of Isma'il (peace be upon him)."
Hadith Referenceالمعجم الكبير للطبراني / باب الصاد / 7525