1 John 4:20

if any one may say -- 'I love God,' and his brother he may hate, a liar he is; for he who is not loving his brother whom he hath seen, God -- whom he hath not seen -- how is he able to love?

1 John 2:4

he who is saying, 'I have known him,' and his command is not keeping, a liar he is, and in him the truth is not;

1 John 2:9

he who is saying, in the light he is, and his brother is hating, in the darkness he is till now;

1 John 3:17

and whoever may have the goods of the world, and may view his brother having need, and may shut up his bowels from him -- how doth the love of God remain in him?

1 John 4:12

God no one hath ever seen; if we may love one another, God in us doth remain, and His love is having been perfected in us;

1 John 2:11

and he who is hating his brother, in the darkness he is, and in the darkness he doth walk, and he hath not known whither he doth go, because the darkness did blind his eyes.

1 Peter 1:8

whom, not having seen, ye love, in whom, now not seeing and believing, ye are glad with joy unspeakable and glorified,

1 John 1:6

if we may say -- 'we have fellowship with Him,' and in the darkness may walk -- we lie, and do not 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 who is saying, 'I have known him,' and his command is not keeping, a liar he is, and in him the truth is not;
1 John 3:17
and whoever may have the goods of the world, and may view his brother having need, and may shut up his bowels from him -- how doth the love of God remain in him?

Not

1 John 4:12
God no one hath ever seen; if we may love one another, God in us doth remain, and His love is having been perfected in us;

General references

Matthew 22:40
on these -- the two commands -- all the law and the prophets do hang.'
Matthew 25:42
for I did hunger, and ye gave me not to eat; I did thirst, and ye gave me not to drink;
John 13:35
in this shall all know that ye are my disciples, if ye may have love one to another.'
John 14:15
'If ye love me, my commands keep,
Hebrews 13:1
Let brotherly love remain;