1 John 4:20

if a man says he loves God, and yet hates his brother, he is a lyar: for he that does not love his brother, who is before his eyes, how can he love God who is invisible?

1 John 2:4

he that says, he knows him, and does not keep his commandments, is a lyar, and an enemy to the truth:

1 John 2:9

he that says, he is in the light, and yet hates his brother, is still in darkness.

1 John 3:17

he that possesses the enjoyments of life, and seeing his brother in want, has no compassion for him, how can he be said to have any divine love?

1 John 4:12

no man hath ever seen God. if we love one another, God dwelleth in us, and our love for him is then sincere.

1 John 2:11

but he that hates his brother, is in darkness, he walks in darkness, and knows not whither he is going, because the darkness hath blinded his eyes.

1 Peter 1:8

whom though you have not seen, you love: and though he is not now the object of your view, yet you believe in him, and triumph with such a laudable transport, as cannot be express'd:

1 John 1:6

if we say that we have communion with him, and walk in darkness, we lye, and do not act sincerely:

Treasury of Scripture Knowledge

Summary

If a man say, I love God, and hateth his brother, he is a liar: for he that loveth not his brother whom he hath seen, how can he love God whom he hath not seen?

Bible References

A man

1 John 2:4
he that says, he knows him, and does not keep his commandments, is a lyar, and an enemy to the truth:
1 John 3:17
he that possesses the enjoyments of life, and seeing his brother in want, has no compassion for him, how can he be said to have any divine love?

Not

1 John 4:12
no man hath ever seen God. if we love one another, God dwelleth in us, and our love for him is then sincere.

General references

Matthew 22:40
these two precepts comprehend the substance of all the law and the prophets.
Matthew 25:42
for I was prest with hunger, and ye gave me no meat: I was thirsty, and ye gave me no drink:
John 13:35
by this mutual love shall all men know that you are my disciples.
John 14:15
if ye love me, keep my commandments.
Hebrews 13:1
Let brotherly love still reign.