This account is close to Matthew 3:13–17 and its parallels in Mark and Luke, with one key difference—the addition of the phrase, “This day I have begotten you.” The Ebionites chose the moment of Jesus’ baptism by John as the key moment in which Jesus became God’s son, rather than the moment of Jesus’ birth. Jesus became God’s son by being “adopted” by him (a “spiritual birth,” so to speak) rather than by being literally fathered by God and born of a virgin. This idea is called adoptionism.
Source: wiktionary