"When the night covered him" means: it sheltered him.

Muhammad said: It is said: The night 'janna' (covered) him, and the night 'ajannahu' (shrouded him); meaning it became dark until it concealed him with its darkness.

"He saw a planet, he said, 'This is my Lord.' But when it set"—meaning it vanished—"he said, 'I do not like those that disappear.'" He was concerned with observation, so he watched the planet until it went and set. He said: And the moon rose, and it was the last night of the month.