Ephesians 1:13

Shepherd of Hermas Similitude Eighth

And the others also he sent into the tower, those, namely, who had returned branches that were green and had offshoots but no fruit, having given them seals.[6]

Tertullian Against Marcion Book V

Hence the apostle refers the statement to himself, that is, to the Jews, in order that he may draw a distinction with respect to the Gentiles, (when he goes on to say:) "In whom ye also trusted, after that ye heard the word of truth, the gospel (of your salvation); in whom ye believed, and were sealed with His Holy Spirit of promise."[764]

Five Books in Reply to Marcion

A pledge;[108]

2 Clement

What then think ye? If one does anything unseemly in the incorruptible contest, what shall he have to bear? For of those who do not preserve the seal"[60]

Acts of Paul and Thecla

I am afraid lest another temptation come upon thee worse than the first, and that thou withstand it not, but be cowardly. And Thecla said: Only give me the seal[18]