John 1:32-33 — And John bare record, saying, I saw the Spirit descending from heaven like a dove, and it abode upon Him.
And I knew Him not: but He that sent me to baptize with water, the same said unto me, Upon whom thou shalt see the Spirit descending, and remaining on Him, the same is He which baptizeth with the Holy Ghost.
This took place right after Jesus' baptism by John.
dove — a type of the Holy Spirit throughout Scripture
He that sent me — God
John knew of Christ, but did not know Him until he saw the Spirit and knew Him to be the Son of God.
Spirit descending — And there shall come forth a rod out of the stem of Jesse, and a Branch shall grow out of his roots: And the Spirit of the Lord shall rest upon Him, the spirit of wisdom and understanding, the spirit of counsel and might, the spirit of knowledge and of the fear of the Lord (Isaiah 11:1-2). The Spirit of the Lord God is upon me; because the Lord hath anointed me to preach good tidings unto the meek; He hath sent me to bind up the brokenhearted, to proclaim liberty to the captives, and the opening of the prison to them that are bound (Isaiah 61:1).
baptizeth with the Spirit — Christ's entire life-giving ministry.
abode — came and stayed