There is no evidence that sprinkling or pouring was ever an apostolic practice but was introduced into Christendom hundreds of years after Christ. JTL16 7.1
The English word baptize is derived from the Greek word bapto, meaning “to dip in or under.” In the New Testament the verb to baptize is used to refer to water baptism of believers (Matthew 3:6; Mark 1:9; and Acts 2:41) as a metaphor of Christ’s suffering and death. Paul’s comment that we are buried by baptism unto death (Romans 6:4) only makes sense if the mode of baptism symbolizes death to the old life and rising to a new life in Christ. JTL16 7.2
The incidents of water baptism in the New Testament involve immersion. We read that John baptized in the river Jordan because “there was much water there.” John immersed Jesus “in the Jordan” and after the baptism Jesus “came up out of the water” (Mark 1:9, 10 RSV). When Philip the evangelist baptized the Ethiopian eunuch, they both “went down into the water” and “came up out of the water” (Acts 8:38, 39). JTL16 7.3