What is the evidence requiring equality among children in a father's gift?

Primary text

Equality among children in a father's gift is established by a specific report where the Prophet (peace be upon him) asked the father if it would please him for his children to be equal in their devotion (birr) to him, and when the father affirmed, the Prophet commanded him to 'make them equal among you.' This specific justification, relating to their equal obligation in dutifulness to the parent, is not present for other relatives.