Well, that is a
belief.
Naturally, I wouldn't walk up to a Christian and say 'Your God is a lesser prophet of my God'. That would most likely be hurtful to them.
But it is freedom of speech that is in question, not freedom of belief. If the situation arises, then yes a Christian and a Muslim can tell each other what they believe but in such a way so as not to offend.
It's easily done. It's been done numerous times on this board easily.
If you like, I can write such a conversation between a Muslim and a Christian.

The sad person that I am.
Actually no I can't. It's too sad. I do have a life you know! Though it may not seem like it. :rollseyes
Regards