Is it true that when Wahshi (The habashi who killed Hamza rAa) came to the Prophet PBUH to declare his Islam, the Prophet PBUH asked him not to show him his face, or something like that? I read several Ahadeeth that mention this, but are they authentic (Sahih) Jazakum Allah'o khairan.

All praise be to Allah, and may His blessings and peace be on His last messenger, Muhammad,

The part of the story of Wahshiy (may Allah be pleased with him) you mentioned about the Prophet (may Allah be pleased with him) asking him to not show him his face is authentically reported by al-Bukhari. This request from the Prophet (may Allah be pleased with him) is because of the pain the he endured upon the killing of Hamza, about whom he said, “I shall never be afflicted with a greater loss after your loss.” However, the Prophet (may Allah be pleased with him) accepted Wahshiy’s Islam, and not only that, he (may Allah be pleased with him) was keen on inviting him to Islam, as reported by at-Tabarani in al-Awsat. Wahshiy (may Allah be pleased with him) was never denied any of his rights as a Muslim. The story of Wahshiy is a remarkable attestation to the fairness of the Messenger of Allah (may Allah be pleased with him) and the vast mercy of Allah (Exalted is He).

Allah knows best.