Al-Husayn b. Ahmad b. Idris narrated to us. He said: My father narrated to us from Ahmad b. Muhammad b. `Isa from al-Hasan b. `Ali b. al-Faddal from al-Hasan b. al-Jahm from al-Fudayl b. Yasar. He said: Al-Sadiq Ja`far b. Muhammad said:

The body does not weaken if one strengthens it with his intention.