Augustine of Hippo — as excerpted in the Catena Aurea on Matthew 1:18

“(De Cons. Evang. ii. 5.) How this was done Matthew omits to write, but Luke relates after the conception of John, In the sixth month the Angel was sent; and again, The Holy Ghost shall come upon thee. This is what Matthew relates in these words, She was found with child of the Holy Ghost. And it is no contradiction that Luke has described what Matthew omits; or again that Matthew relates what Luke has omitted; that namely which follows, from Now Joseph her husband being a just man, to that place where it is said of the Magi, that They returned into their own country another way. If one desired to digest into one narrative the two accounts of Christ’s birth, he would arrange thus; beginning with Matthew’s words, Now the birth of Christ was on this wise; (Luke 1:5.) then taking up with Luke, from There was in the days of Herod, to, Mary abode with her three months, and returned to her house; then taking up again Matthew, add, She was found with child of the Holy Ghost. (Mat. 1:10.)”