John 1:8

That one was not the light, but [came] in order that he could testify about the light.

John 1:20

And he confessed--and he did not deny, and confessed--"I am not the Christ!"

John 3:28

You yourselves testify about me that I said, 'I am not the Christ, but I am sent before that one.'

Acts 19:4

And Paul said, "John baptized [with] a baptism of repentance, telling the people that they should believe in the one who was to come after him--that is, in Jesus."

Treasury of Scripture Knowledge

Summary

He was not that Light, but was sent to bear witness of that Light.

General references

Bible References

That light

John 1:20
And he confessed--and he did not deny, and confessed--"I am not the Christ!"
John 3:28
You yourselves testify about me that I said, 'I am not the Christ, but I am sent before that one.'
Acts 19:4
And Paul said, "John baptized [with] a baptism of repentance, telling the people that they should believe in the one who was to come after him--that is, in Jesus."

General references

Mark 11:30
The baptism of John--was [it] from heaven or from men? Answer me!"
Acts 13:24
Before {his coming} John had publicly proclaimed a baptism of repentance to all the people of Israel.