The Messenger of Allah ﷺ said, "The warrior who fights receives his reward, and the one who equips another to fight in his place receives his own reward as well as the reward of the warrior."
حدثنا إسحاق بن عيسى حدثنا ليث حدثني حيوة يعني ابن شريح عن ابن شفي الأصبحي عن أبيه
قال رسول الله ﷺ للغازي أجره وللجاعل أجره وأجر الغازي
Its chain of transmission is sahih. Ibn Shufayy is Husayn bin Shufayy al-Asbahi, a trustworthy Egyptian follower of the companions. Ibn Hibban and Ajli confirmed his reliability, and Bukhari mentioned him in al-Kabir 1/2/379, saying, "He heard from Abdullah bin Amr," and narrated from him with his chain of transmission, saying, "We were with Abdullah bin Amr," and so on. His father, Shufayy, was already discussed in entry 7563.This hadith was narrated by Abu Dawud, 2526 (2:323 of Awn al-Mabud), by way of Hajjaj bin Muhammad and Ibn Wahb, both from Layth bin Saad, with this same chain of transmission. The name of the companion in this hadith appears in al-Muntaqa, 4197, as Abdullah bin Umar, but this is a printing error.Al-Jaail is an active participle from the expression "he set for him a jul or jaalah," with the jeem vowelled fatha as a verbal noun and vowelled damma as a noun of instance, meaning he set a wage for him. Al-Julyah and al-Jaalah, with the jeem vowelled fatha in both, and with damma or kasra in the second word, refer to the wage given for that purpose. Al-Jaail is the one who gives it, and al-Mujtail is the one who takes it. What is meant is that when military service is decreed obligatory upon a man, he gives another man something so that he goes out in his place.There has been disagreement over whether this is permissible, and Khattabi and those who followed him have clarified the difference of opinion on it. In my view, if a man has a legitimate excuse that keeps him from military service and he supports a fighter with his wealth, then he has the reward of the fighter. But if military service becomes specifically obligatory upon a man and he stays behind from it, hiring another man with his wealth in his place, then this is not permissible.