Musa learned that there was a servant of Allah who had been given knowledge that he did not have. He found him at the meeting of the two seas and said: may I follow you so that you teach me some of the right guidance you have been taught? He said: you will not be able to be patient with me. Musa promised patience, on the condition that he would ask nothing until told.
Three events
They boarded a boat, and the servant made a hole in it. Musa cried: would you drown its people? He was reminded of the condition.
Then the servant killed a boy. Musa could not hold back: you have killed an innocent soul! Again he was reminded.
Then in a town they asked for food and no one would host them. Finding a wall about to collapse, the servant set it straight. Musa said: you could have taken a wage for it. He said: this is where we part; now hear the explanation.
The explanation
The boat belonged to poor people; ahead was a king who seized every good boat by force — so it was made defective. The boy's parents were believers, and it was feared he would burden them with defiance and disbelief; Allah would give them a better child. And the wall belonged to two orphan boys whose father had been righteous; their treasure lay beneath it, and Allah willed that they reach maturity and bring it out.