The story
Harun is the only prophet in the Qur'an who became one because another prophet asked. Standing before the mission of his life, Musa prayed: 'Appoint for me a minister from my family: Harun, my brother. Increase through him my strength' (20:29-31), praising his brother's superior eloquence (28:34). The answer, 'We will strengthen your arm through your brother' (28:35), made brotherhood itself a prophetic institution.
He stood beside Musa through every round with Pharaoh, and then faced his own crucible alone: left in charge while Musa was on Sinai, he watched the people melt their jewelry into a calf. He pleaded, warned, and was nearly killed for it (7:150); when Musa returned in fury and seized him, Harun's answer, 'O son of my mother, do not seize my beard or my head' (20:94), chose the unity of the ummah over his own vindication until the matter could be judged rightly.
The Prophet Muhammad ﷺ sealed his standing forever when he told Ali: 'You are to me as Harun was to Musa, except that there is no prophet after me.'