Another route
Aḥmad said: ʿAbd al-Razzāq narrated to us; Maʿmar narrated to us, from al-Zuhrī, who informed me that al-Qāsim b. Muḥammad said:
Abū Hurayrah and Kaʿb once sat together. Abū Hurayrah began recounting to Kaʿb what he had heard from the Prophet ﷺ, while Kaʿb informed Abū Hurayrah of what was in the earlier scriptures. Abū Hurayrah said: The Prophet ﷺ said, “Every prophet has one supplication that is certainly answered, and I have kept my supplication in reserve as an intercession for my ummah on the Day of Resurrection.”
Aḥmad alone transmitted this ḥadīth; its chain is sound according to the criteria of both Imām al-Bukhārī and Imām Muslim, and none of the authors of the six canonical collections recorded it through this route (1).

Another route
Aḥmad said: Yaḥyā narrated to us, from Shuʿbah; and Muḥammad b. Jaʿfar—Shuʿbah narrated to us, from Muḥammad b. Ziyād, from Abū Hurayrah. Ghundar, in his narration, said: I heard Abū Hurayrah report from the Prophet ﷺ: “Indeed, every prophet had a supplication which he offered, and I wish—if Allah wills—to store up my supplication as an intercession for my ummah on the Day of Resurrection.” Ibn Jaʿfar added, “for my ummah.”
Muslim also recorded it from Shuʿbah through this chain (2).

Another route
Aḥmad said: ʿAbd al-Razzāq narrated to us; Maʿmar narrated to us, from Hammām b. Munabbih, who narrated from Abū Hurayrah, who said: The Messenger of Allah ﷺ said, “Every prophet has a supplication that is granted; I wish, if Allah wills, to save my supplication as an intercession for my ummah on the Day of Resurrection.”
This chain is sound according to the criteria of both Imām al-Bukhārī and Imām Muslim, yet they did not include it (3).

Another route
Muslim said: Qutaybah b. Saʿīd narrated to us; Jarīr narrated to us, from ʿUmārah—who is Ibn al-Qaʿqāʿ—from Abū Zurʿah, from Abū Hurayrah, [who said: The Messenger of Allah ﷺ said]: “Every prophet has one accepted supplication which he calls upon…"