A.T. Robertson Commentary Matthew 11:2

"Now when John heard in the prison the works of the Christ, he sent by his disciples" — Matthew 11:2 (ASV)

John heard in the prison (ο δε Ιωανης ακουσας εν τω δεσμωτηριω). Probably (Luke 7:18) the raising of the son of the widow of Nain. The word for prison here is the place where one was kept bound (Acts 5:21,23; 16:26). See Mt 4:12. It was in Machaerus east of the Dead Sea which at this time belonged to the rule of Herod Antipas (Jos. Ant. XVIII. v.2). John's disciples had access to him. So he sent word by (δια, not δυο as in Lu 7:19) them to Jesus.