Sahih Muslim 1019
Sahih Muslim · Book 12: The Book of Zakat · The virute of giving gifts
It is narrated on the authority of Abu Huraira (that the Messenger of Allah) said:
حَدَّثَنَا زُهَيْرُ بْنُ حَرْبٍ ، حَدَّثَنَا سُفْيَانُ بْنُ عُيَيْنَةَ ، عَنْ أَبِي الزِّنَادِ ، عَنِ الأَعْرَجِ ، عَنْ أَبِي هُرَيْرَةَ ، يَبْلُغُ بِهِ " أَلاَ رَجُلٌ يَمْنَحُ أَهْلَ بَيْتٍ نَاقَةً تَغْدُو بِعُسٍّ وَتَرُوحُ بِعُسٍّ إِنَّ أَجْرَهَا لَعَظِيمٌ " .
Of course the person who gives to the family a she-camel as a gift, which gives milk morning and evening equal to a large bowl, its reward (the reward of the gift) is great.