Is it obligatory to refrain from determining whether Joshua the son of Nun was a prophet or not, and what is the ruling on one who refrains from doing so, especially if the refraining is based on the possibility of doubt in the evidence, such as it being solitary (Ahad) narrations?

The hadith: "A prophet among the prophets raided..." is confirmed in the Two Sahihs. Scholars have inferred that this prophet is Yusha' ibn Nun, but the hadiths that name him Yusha' ibn Nun as being مرفوعة (traced back) to the Prophet, peace and blessings be upon him, are weak and have discrepancies in their chain of narration (sanad), due to Abu Bakr ibn Ayyash being the sole narrator of them, and the instability of his memory.

The correct view is that the naming of Yusha' ibn Nun originates from Ka'b al-Ahbar, attributed to him (موقوفة عليه), and is not مرفوعة (traced back) to the Prophet, peace and blessings be upon him. As for the prophethood of Yusha' ibn Nun, it is agreed upon by the People of the Book, and it is relied upon by those who authenticated the narration of Abu Bakr ibn Ayyash or depended on the statement of Ka'b al-Ahbar.