Three things only a prophet would know

When word reached Madinah that the Prophet ﷺ had arrived, people rushed out to see him. Abdullah ibn Salam was among the Jewish scholars of the city, known for his learning, and he went to test him rather than simply to look.

He said he would ask about three things that nobody but a prophet could know: what the first sign of the Hour would be, what the first food would be that the people of Paradise are given, and why a child sometimes resembles its father's side of the family and sometimes its mother's.

The Prophet ﷺ answered him: the first sign of the Hour would be a fire that gathers people from the east to the west; the first food of the people of Paradise would be a portion of fish liver; and which parent a child resembles turns on whichever parent's contribution to conception comes first.

Ibn Salam said that this confirmed it, and that no one but a prophet could have answered as he had. But he had one request. His people, he said, were prone to slander, and he asked the Prophet ﷺ to question them about his standing before they learned that he had accepted Islam — otherwise, he warned, they would speak against him.

The Jewish scholars of Madinah were brought and asked what kind of man Abdullah ibn Salam was among them. They answered that he was the best of them and the son of the best of them, their most learned man and the son of their most learned man.

The Prophet ﷺ then asked what they would think if Abdullah ibn Salam accepted Islam. They said they hoped Allah would spare him from that.

At that, Ibn Salam came out and declared that there is no god but Allah and that Muhammad is His messenger. The same people who had just praised him then said he was the worst of them and the son of the worst of them, and went on to speak against him.

Ibn Salam said this was exactly what he had feared. The whole exchange is preserved in Sahih al-Bukhari.