1 John 4:20

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

1 John 2:4

He that saith, I know Him, and keepeth not his commandments, is a liar, and the truth is not in him.

1 John 2:9

Now he that saith he is in the light, and hateth his brother, is still in darkness:

1 John 3:17

But if any one, who hath the good things of the world, seeth his brother in want, and shutteth up his bowels from him, how dwelleth the love of God in him?

1 John 4:12

No one hath ever seen God: but if we love one another, God dwelleth in us and his love is perfected in us.

1 John 2:11

But he, that hateth his brother, is in darkness, and walketh in darkness, and knoweth not where he goeth, because the darkness hath blinded his eyes.

1 Peter 1:8

whom having not seen ye love; in whom, though now ye see Him not, yet believing ye rejoice with joy ineffable and full of glory; receiving the end of your faith,

1 John 1:6

If we say that we have communion with Him, and walk in darkness, we lie and do not practise the truth:

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 saith, I know Him, and keepeth not his commandments, is a liar, and the truth is not in him.
1 John 3:17
But if any one, who hath the good things of the world, seeth his brother in want, and shutteth up his bowels from him, how dwelleth the love of God in him?

Not

1 John 4:12
No one hath ever seen God: but if we love one another, God dwelleth in us and his love is perfected in us.

General references

Matthew 22:40
On these two precepts depend all the law and the prophets.
Matthew 25:42
for I was famishing, and ye gave me nothing to eat; I was a-thirst, and ye gave me no drink;
John 13:35
if ye have mutual love to each other.
John 14:15
If ye love me, keep my commandments. And I will ask the Father,
Hebrews 13:1
Let brotherly love continue.