More than one scholar has stated that Uthman ibn Maz'un was the first person buried in al-Baqi'. Yet I have not found this transmitted through a connected chain that may be adduced as evidence. The strongest report I have found is that which Ibn Sa'd related (3/397) through al-Waqidi himself, who said: Muhammad ibn Abd Allah informed us, from al-Zuhri, from Abd Allah ibn Amir ibn Rabi'ah, who said:

“The first Muslim to be buried in al-Baqi' was Uthman ibn Maz'un …”

This Ibn Rabi'ah was born during the lifetime of the Prophet, peace and blessings be upon him; however, the chain to him is utterly unsound, because al-Waqidi is abandoned, as mentioned above. His teacher Muhammad ibn Abd Allah—namely, Ibn Abi Sabrah, Abu Bakr al-Madini—was described by al-Dhahabi in al-Mizan as follows:

“Ahmad said: ‘He used to fabricate hadiths.’”

Ibn Abd al-Barr also mentioned it through al-Waqidi, from [Ibn] Abi Sabrah, from Asim ibn Ubayd Allah, from Ubayd Allah ibn Abi Rafi', who said … and then cited it. This Ibn Abi Rafi' was a trustworthy Successor.

Ibn Sa'd then related (3/612), likewise through al-Waqidi, who said: Abd al-Jabbar ibn Umarah informed us, from Abd Allah ibn Abi Bakr ibn Muhammad ibn Amr ibn Hazm, who said:

“The first person buried in al-Baqi' was As'ad ibn Zurarah.”

Al-Waqidi said: “This is the view of the Ansar. The Muhajirun, however, say that the first person buried in al-Baqi' was Uthman ibn Maz'un.”

Ibn Shabbah also cited it in his History (1/96), attributing it without a complete chain to al-Waqidi through another chain to him, in a similar but abridged form that does not mention Uthman’s burial.