Was the israeeli who helped Musa alayhissalam a muslim?
“And he (Musa alayhissalam) entered the city at a time of unawareness of its people, and he found there two men fighting, one of his party (his religion, from the children of Israel), and the other of his foes. The man of his own party asked him for help against his foe, so Moses struck him with his fist and killed him. He said, “This is of Satan’s doing, verily, he is a plain misleading enemy.”He said: “My Lord! Verily, I have wronged myself, so forgive me.” Then He forgave him. Verily, He is the Oft-Forgiving, the Most Merciful.
He said: “My Lord! For that with which You have favored me, I will never more be a helper for the Mujrimeen (criminals, disobedient to Allah, polytheists, sinners, etc.)!”
So he became afraid, looking about in the city (waiting as to what will be the result of his crime of killing), when behold, the man who had sought his help the day before, called for his help again. Moses said to him: “Verily, you are a plain misleader!” Then when he decided to seize the man who was an enemy to both of them, the man said: “O Moses! Is it your intention to kill me as you killed a man yesterday? Your aim is nothing but to become a tyrant in the land, and not to be one of those who do right.”
And there came a man running, from the farthest end of the city. He said: “O Moses! Verily, the chiefs are taking counsel together about you, to kill you, so escape. Truly, I am to you of those who give sincere advice.”
So he escaped from there, looking about in a state of fear. He said: “My Lord! Save me from the people who are Zalimeen (polytheists, and wrong-doers)!” (Ch 28:15-21 Quran)
Yes, he was a secret believer in Musa Alayhi Salam. When the secret was disclosed, Firaun tried to murder him. But he fled to the mountains and Allah protected him.
It is stated in Tafseer Roohul Ma’ani (p.72 vol 24) under the Ayat:
“Then Allah saved him from the evil plots which they had devised…” (40:45)
Abdullah Ibn Abbas (RA) says, “When this mu’min revealed his Iman, Firaun attempted to murder him. So he fled to a mountains and Firaun sent a thousand men to capture him. They saw him praying while beasts were protecting him. When they went closer, the beasts attacked them. Some fell off the mountains, others were devoured by the beasts and some died in the mountains due to thirst. Those who returned to Firaun were blamed with failure and punished by Firaun.”
In fact, in the Quran there is a Surah named after this believer. It’s called Surah al-Mu’min (Surah no.40). It’s also called Surah Ghaafir.