Does it prove that someone was not a prophet if he was killed?

No. The Holy Qur’an itself says that prophets were killed, and it even speaks of the possibility that the Holy Prophet Muhammad (saw) might be killed.

Some people think a true prophet cannot be killed by other people. If it happens, they say, it shows that God was against him. Yet there is no basis for such a standard. Before building a judgement on it, we have to ask where it comes from.

The Holy Qur’an clearly rejects this idea. The first verse above says that all Messengers before the Holy Prophet Muhammad (saw) have passed away. It then asks the believers whether they would turn back if he died or was slain. If being killed by human hands proved someone a false prophet, the Holy Qur’an could not speak like this. The second verse, too, speaks of people who seek to kill prophets, and the guilt is theirs alone.

The idea usually comes from a misunderstood verse. It says that if someone attributed words to God, God would seize him by the right hand and sever his life artery. Some read this to mean that anyone who is killed must be a liar. But that reading contradicts the first verse, so it cannot be right.

What it means is that God utterly destroys the cause of a false prophet. His claim collapses, and everyone sees that God is not with him. With a true prophet it is the other way round. Even if his life is taken, his message lives on and grows. What matters is not how a prophet dies, but what becomes of his work.