Abu 'Umayr wal nughayr

It is proven in al-Saheehayn (al-Bukhaari, 5778; Muslim, 2150) that the brother of Anas ibn Maalik through his mother was called Abu ‘Umayr and he had a bird who was called al-nughayr. 

The bird died and the child grieved for it (and was really sad), and the Prophet (peace and blessings of Allaah be upon him) tried to cheer him up by saying, “O Abu ‘Umayr, what happened to al-nughayr?” 

The nughayr is a small bird like a sparrow, or it was said that it is a nightingale. 

This hadeeth is taken as evidence that it is permissible to keep birds, because the Prophet (peace and blessings of Allaah be upon him) did not denounce Abu ‘Umayr for doing so. 

See Fath al-Baari, 10/548

Al-Nawawi said: 

The nughayr is a small bird. 

This hadeeth teaches us many things, such as being kind to small children. This demonstrates the good character of the Prophet (peace and blessings of Allaah be upon him) and how he was of noble character and humble. 

Sharh Muslim, 14/129

The Prophet (peace be upon him) used to joke with the small child of one of the Sahaba, a boy called Abu 'Umayr, who had a small bird he used to play with. One day he saw the child looking sad, so he said, "Why do I see Abu 'Umayr looking sad?" The Sahaba told him, "The nughar [a small bird, like a sparrow] which he used to play with has died, O Messenger of Allah"..

The Prophet (peace and blessings of Allaah be upon him) began to gently joke with the child, saying, "O Abu Umayr, what happened to the nughayr?" [Nughayr: baby form of nughar. In Arabic, this is a play on words, because of the rhyme between the boy's name and that of the bird].  

Source: This story was reported in Hayat al-Sahabah, 3/149.