1 John 5:6
This is the one who came through water and blood, Jesus Christ, not by water alone, but by water and blood. The Spirit is the one that testifies, and the Spirit is truth.
NAB Commentary - 1 John 5:6
*[6-12] Water and blood (1Jo 5:6) refers to Christ's baptism (Mat 3:16-17) and to the shedding of his blood on the cross (Joh 19:34). The Spirit was present at the baptism (Mat 3:16; Mar 1:10; Luk 3:22; Joh 1:32,34). The testimony to Christ as the Son of God is confirmed by divine witness (1Jo 5:7-9), greater by far than the two legally required human witnesses (Deu 17:6). To deny this is to deny God's truth; cf Joh 8:17-18. The gist of the divine witness or testimony is that eternal life (1Jo 5:11-12) is given in Christ and nowhere else. To possess the Son is not acceptance of a doctrine but of a person who lives now and provides life.
+Joh 15:26; 19:34
John 15:26
"When the Advocate comes whom I will send you from the Father, the Spirit of truth that proceeds from the Father, he will testify to me.
John 19:34
but one soldier thrust his lance into his side, and immediately blood and water flowed out.