He—may Allah Most High have mercy on him—was asked:

A man gave something to one of his children but gave nothing to the other because the first was obedient to him. May he favor the one who obeys him and deprive the one who disobeys him? The son who received nothing swore an oath invoking divorce that he would not speak to his father unless his father treated him equally. Is there a way out for him? Does an oath invoking divorce have the same status as other oaths, or not?

He replied:

A man must treat his children justly, as Allah and His Messenger have commanded. It is established in the two Sahīh collections that the Prophet, may Allah bless him and grant him peace, addressed Bashīr ibn Saʿd when he gave his son al-Nuʿmān a gift and came to the Prophet, may Allah bless him and grant him peace, to ask him to witness it. He said to him:

“Fear Allah and treat your children justly.”

He also said:

“Do not ask me to witness this, for I do not bear witness to injustice.”

And he told him, “Take it back.” So Bashīr took it back. He also told him, by way of warning:

“Do not call anyone other than me to witness this.”

However, he may single out one of them on grounds recognized by Islamic law: for example, if one is needy and obedient to Allah, while the other is wealthy and disobedient, using his wealth to facilitate sin. If he gives to the one Allah has commanded him to give to, and withholds from the one Allah has commanded him to withhold from, he has done well.