'Sandal strap' in the Bible

His announcement was, "There is One coming after me mightier than I--One whose sandal-strap I am unworthy to stoop down and unfasten.

he answered the question by saying to them all, "As for me, I am baptizing you with water, but One mightier than I is coming, whose very sandal-strap I am not worthy to unfasten: He will baptize you in the Holy Spirit and with fire.

He who is to come after me, and whose sandal-strap I am not worthy to unfasten."