8 In fine, He calls those the children of Abraham whom He sees to be laborious in aiding and nourishing the poor. For when Zacchaeus said, “Behold, the half of my goods I give to the poor; and if I have done any wrong to any man, I restore fourfold,” Jesus answered and said, “That salvation has this day come to this house, for that he also is a son of Abraham.” For if Abraham believed in God, and it was counted unto him for righteousness, certainly he who gives alms according to God's precept believes in God, and he who has the truth of faith maintains the fear of God; moreover, he who maintains the fear of God considers God in showing mercy to the poor.
For he labours thus because he believes— because he knows that what is foretold by God's word is true, and that the Holy Scripture cannot lie— that unfruitful trees, that is, unproductive men, are cut off and cast into the fire, but that the merciful are called into the kingdom. He also, in another place, calls laborious and fruitful men faithful; but He denies faith to unfruitful and barren ones, saying, “If you have not been faithful in the unrighteous mammon, who will commit to you that which is true? And if you have not been faithful in that which is another man's, who shall give you that which is your own?”
Source: The Treatises of Cyprian (New Advent)