Grading: Its chain is da'if. Mu'ammal bin Isma'il is "of poor memory" (sayyi' al-hifz), and he erred in the chain of this report: he made it a statement of the Successor 'Abd al-Rahman bin Sabit, whereas in fact it is the narration of his brother "Muhammad bin Sabit", "marfu' mursal", as in the narration of Abu Sa'id the freed slave of Banu Hashim and Yazid bin Harun from Hammad bin Salamah. Hammad heard from 'Ata' bin al-Sa'ib before his confusion (ikhtilat), so this is what is correct in 'Ata''s narration. Even so, it is "da'if", because Muhammad bin Sabit is "majhul" (unknown) and the narration is mursal. Jarir bin 'Abd al-Hamid agreed with Mu'ammal, but Jarir heard from 'Ata' after his confusion, and his inconsistency (once as 'Abd al-Rahman's statement, once from Ibn Sabit as marfu' mursal) is the effect of that confusion, so Jarir's corroboration counts for nothing.

Details of the narration: Al-Azraqi narrated in "Akhbar Makkah" 1/ 68 by way of 'Abdullah bin 'Uthman bin Khuthaym, from 'Abd al-Rahman bin Sabit, from 'Abdullah bin Damrah al-Saluli, who said: "Between the Corner, the Maqam and Zamzam are the graves of ninety-nine prophets who came as pilgrims and were buried there."
Conclusion: This is what is "mahfuz" (preserved) from 'Abd al-Rahman bin Sabit, and it is his narration from 'Abdullah bin Damrah as a "maqtu'" statement (of 'Abdullah bin Damrah). So it appears that the mistake here occurred in mentioning 'Abd al-Rahman bin Sabit. And Allah knows best.

Reference / Source: Ibn 'Asakir narrated it in "Tarikh Dimashq" 62/ 287-288 by way of 'Abdullah bin Abi Ghassan al-Kufi, from Jarir bin 'Abd al-Hamid, from 'Ata' bin al-Sa'ib, likewise.

Reference / Source: Ibn Jarir al-Tabari narrated it in his "Tafsir" 1/ 199 from Muhammad bin Humayd, from Jarir bin 'Abd al-Hamid, from 'Ata' bin al-Sa'ib, from Ibn Sabit, that the Prophet (peace and blessings be upon him) said … and he mentioned it.

Reference / Source: Al-Azraqi narrated it in "Akhbar Makkah" 1/ 68 by way of Abu Sa'id ('Abd al-Rahman bin 'Abdullah, the freed slave of Banu Hashim), from Hammad bin Salamah, from 'Ata', from Muhammad bin Sabit, from the Prophet (peace and blessings be upon him).

Corroborating chains and supporting reports: Yazid bin Harun corroborated Abu Sa'id the freed slave of Banu Hashim, as in al-Bukhari's "al-Tarikh al-Kabir" 1/ 104.

Reference / Source: Muhammad bin al-Hasan al-Shaybani narrated it in "al-Athar" (266) from Imam Abu Hanifah, from 'Ata' bin al-Sa'ib, as his own statement, in similar wording.