Augustine of Hippo

So if you are afraid your son won't take care of you once he has his hands on the money, you are in fact making filial piety a commodity for sale, not a quality to be loved. How much better a poor man's son, the son, for instance, of an old man in the direst poverty, who expects nothing from his father because he hasn't got anything he can leave him but who all the same supports his father with his labor and the sweat of his brow. …

Sermon 45.2 ↗

Ambrose of Milan

The formation of the children is then the prerogative of the parents. Therefore honor your father, that he may bless you. Let the godly man honor his father out of gratitude and the ingrate do so on account of fear. Even if the father is poor and does not have plenty of resources to leave to his sons, still he has the heritage of his final blessing with which he may bestow the wealth of sanctification on his descendants. And it is a far greater thing to be blessed than it is to be rich.

The Patriarchs 1.1 ↗

Jerome

[The Lord] declares that [this commandment] is to be interpreted not of mere words, which while offering an empty show of regard may still leave a parent's wants unrelieved, but by the actual provision of the necessaries of life. The Lord commanded that poor parents should be supported by their children and that these should pay them back when old for those benefits which they had themselves received in their childhood.

Letter 123.6 ↗