This 4811 [custom], of not bending the knee upon Sunday, is a symbol of the resurrection, through which we have been set free, by the grace of Christ, from sins, and from death, which has been put to death under Him. Now this custom took its rise from apostolic times, as the blessed Irenæus, the martyr and bishop of Lyons, declares in his treatise On Easter, in which he makes mention of Pentecost also; upon which [feast] we do not bend the knee, because it is p. 570 of equal significance with the Lord’s day, for the reason already alleged concerning it.
Taken from a work (Quæs. et Resp. ad Othod.) ascribed to Justin Martyr, but certainly written after the Nicene Council. It is evident that this is not an exact quotation from Irenæus, but a summary of his words. The “Sunday” here referred to must be Easter Sunday. Massuet’s emendation of the text has been adopted, ἐπ’ αὐτοῦ for ἐπ’ αὐτῶν.