Is this halal or haram? If I say to someone "I love Allah more than you love Him. He belongs to me, not to you."

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

This statement in question involves several Islamic violations, among which is that it is a kind of bad conduct when addressing people while Allah Says (what means):

• {And speak to people good [words].} [Quran 2:83]

• {And tell My servants to say that which is best. Indeed, Satan induces [dissension] among them. Indeed Satan is ever, to mankind, a clear enemy.} [Quran 17:53]

This statement also includes praising oneself by claiming to love Allah more than other people do.

As regards your saying: “Allah belongs to me, not to you.", then this is restricting the vast Mercy and Favor of Allah upon His Slaves.

When a Bedouin said: “'O Allah, have mercy upon me and Muhammad and do not have mercy upon anyone else'; the Prophet said to him: 'You have limited something vast," meaning the Mercy of Allah. [Al-Bukhaari]

Tuhfatul-Ahwathi reads: “It means you have restricted what Allah has made vast and you appropriated it to yourself and excluded everyone else.” [End of quote]

You have also restricted (the love of) Allah to yourself and excluded everyone else. In addition to this restricting the love and mercy of Allaah, this may also include lying. Just like Allah is your Lord and the Disposer of your affairs, He is also the Lord of others and the Disposer of their affairs.

Therefore, you should not exaggerate by restricting the vast Mercy of Allah and His Favor.

Allah knows best.