28 But now I must remind you of a few things out of many which are spoken concerning the Son's sitting at the right hand of the Father. For the hundred and ninth Psalm says plainly, The Lord said unto my Lord, Sit on My right hand, until I make Your enemies Your footstool. And the Saviour, confirming this saying in the Gospels, says that David spoke not these things of himself, but from the inspiration of the Holy Ghost, saying, How then does David in the Spirit call Him Lord, saying, The Lord said unto my Lord, Sit on My right hand? And the rest. And in the Acts of the Apostles, Peter on the day of Pentecost standing with the Eleven, and discoursing to the Israelites, has in very words cited this testimony from the hundred and ninth Psalm.
Source: Catechetical Lectures (New Advent)