Is the reward equal for someone who quits smoking solely because it is forbidden (haram) and for someone who quits because it is forbidden and harmful to the body, and is there a reward for someone who quits only because of its harm?

One is not rewarded for abandoning a sin unless the abandonment is for the sake of Allah and out of fear of Him. So, whoever abandons a sin merely out of fear of its worldly harm, without intending to please Allah, will not be rewarded for it, even though abandoning sin is good in all circumstances. Scholars have stated that intending to abandon a sin for the sake of Allah while also considering a worldly purpose – such as preserving health – does not nullify the reward, but rather diminishes it, based on the saying of Ibn Taymiyyah: "If one abandons it out of fear of Allah, Allah will record it for him as a complete good deed." The summary of this is that whoever abandons smoking solely because of its prohibition will have a greater reward than someone who abandons it both for its prohibition and out of fear of its harm to the body. Both of them are rewarded. However, whoever abandons it only for its harm to the body, without any consideration for pleasing Allah, will not be rewarded.