Kitab al-Kafi
It is narrated in "Kitab al-Kafi" that Imam Musa al-Kadhim would accept one dirham from the people, although he was one of the wealthiest in the city of Medina, to purify them. He compares this to Allah asking His creatures to lend to Him from their property, not because He is need, but rather it is His right as appointed guardian over His creatures.