Abu Bakr wrote to me what Allah had ordered His Apostle (about Zakat) which goes: Neither an old nor a defected animal, nor a male-goat may be taken as Zakat except if the Zakat collector wishes (to take it).  

أَنَّ أَبَا بَكْرٍ ؓ كَتَبَ لَهُ {الصَّدَقَةَ} الَّتِي أَمَرَ اللَّهُ رَسُولَهُ ﷺ وَلاَ يُخْرَجُ فِي الصَّدَقَةِ هَرِمَةٌ وَلاَ ذَاتُ عَوَارٍ وَلاَ تَيْسٌ إِلاَّ مَا شَاءَ الْمُصَدِّقُ