You are in the same position with relation to me as Aaron (Harun) was in relation to Moses but with (this explicit difference) that there is no prophet after me. Sa'd said: I had an earnest desire to hear it directly from Sa'd, so I met him and narrated to him what (his son) Amir had narrated to me, whereupon he said: Yes, I did hear it. I said: Did you hear it yourself? Thereupon he placed his fingers upon his ears and said: Yes, and if not, let both my ears become deaf.
The Book of the Merits of the Companions - Sahih Muslim 2404 a
This narration establishes the unique status of 'Ali ibn Abi Talib (may Allah be pleased with him) in relation to the Prophet Muhammad (peace be upon him). The comparison to Harun (Aaron) and Musa (Moses) signifies that 'Ali holds a position of vicegerency, assistance, and close companionship, similar to how Harun was to Musa.
The crucial qualification "but there is no prophet after me" definitively closes the door of prophethood while affirming 'Ali's temporal authority and special rank among the Companions. This hadith is a cornerstone in understanding the virtues of Ahl al-Bayt (the Prophet's household).
The meticulous chain of narration, with Sa'd's emphatic testimony placing fingers on his ears, demonstrates the rigorous standards of hadith verification employed by early Muslim scholars to preserve the Prophet's authentic teachings.