Of Saint John Almsgiver, recorded by the ensemble Jerycho, and was moved by the Communion, the text of which is as follows.
Qui pronus est ad misericordiam, benedicetur; de panibus enim suis dedit pauperi.
What I can find in Cantus Index is this, number h03307, from the area of León in the second half of the 10th century.
Felix qui pronus est ad misericordiam benedicetur de panibus suis dedit pauperibus.
I´m not myself able to trace the antiphon's spread throughout Europe-- from where to where, I wonder; from the Near East to Eastern Europe thence to Spain? but probably from the East to Spain and thence to Poland?-- but I should dearly love to read the work of someone who has.