The Prophet ﷺ said: No sadaqah is due on a horse or a slave except that given at the breaking of the fast (at the end of Ramadan).  

عَنِ النَّبِيِّ ﷺ قَالَ لَيْسَ فِي الْخَيْلِ وَالرَّقِيقِ زَكَاةٌ إِلاَّ زَكَاةُ الْفِطْرِ فِي الرَّقِيقِ  

The Messenger of Allah ﷺ as saying No sadaqah is due from a Muslim on his slave or his horse.  

أَنَّ رَسُولَ اللَّهِ ﷺ قَالَ لَيْسَ عَلَى الْمُسْلِمِ فِي عَبْدِهِ وَلاَ فِي فَرَسِهِ صَدَقَةٌ