Yahya related to me from Malik from Yahya ibn Said that Muadh ibn
Jabal said, "There are two military expeditions. There is one military
expedition in which valuables are spent, the contributor is willing,
the authorities are obeyed, and corruption is avoided. That military
expedition is all good. There is a military expedition in which
valuables are not spent, the contributor is not willing, the
authorities are not obeyed, and corruption is not avoided. The one who
fights in that military expedition does not return with reward."
Muwatta Malik Book 21, Hadith 45