By this we know that we abide in Him, and He in us, because He has given us of His Spirit.
1 John 4:13
Surrounding context
4:12 No one has seen God at any time. If we love one another, God abides in us, and His love has been perfected in us.
4:13 By this we know that we abide in Him, and He in us, because He has given us of His Spirit.
4:14 And we have seen and testify that the Father has sent the Son as Savior of the world.