Ibn Ishaq محمد بن إسحاق بن يسار‎ · The Book of Zakah

"The Messenger of Allah said: '(On the Day of Resurrection) camels will come to their owner in the best state of health that they ever had (in this world) and if he did not pay what was due on them, they will trample him with their hooves. Sheep willcome to their owner in the best state of health that they ever had (in this world) and if he did not pay what was due on them, they will trample him…

"The Muslim does not have to pay Sadaqah on his slave or his horse."