Abī Ḥabīb, from Sālim b. Abī Sālim, from Muʿāwiyah b. Muʿattib (1) al-Hudhalī, from Abū Hurayrah, who said that he heard him say:

I asked the Messenger of Allah ﷺ, “What response has your Lord given you about intercession?” He replied:

“By Him in whose hand is the soul of Muhammad, I truly supposed you would be the first of my community to ask me about that, because I have seen how eager you are for knowledge. By Him in whose hand is the soul of Muhammad, my anxiety over their being held back at the gates of Paradise weighs on me more than the completion of my intercession. My intercession is for anyone who testifies that there is no deity but Allah, doing so sincerely—his heart confirming his tongue and his tongue confirming his heart.”

Aḥmad alone related this ḥadīth through this chain (3).

Another route
Aḥmad said: I read before ʿAbd al-Raḥmān, on the authority of Mālik; and Isḥāq narrated to us—Mālik narrated to us—from Abū al-Zinād, from al-Aʿraj, from Abū Hurayrah, that the Messenger of Allah ﷺ said:

“Every prophet has a supplication [with which he prays], and I wish to reserve my supplication as an intercession for my ummah in the Hereafter.” Isḥāq added, “So I wished to reserve…”

Al-Bukhārī also recorded it from Mālik through this chain (4).

Another route
Muslim said: Ḥarmalah b. Yaḥyā narrated to me; Ibn Wahb informed us; Yūnus narrated to me, from Ibn Shihāb, that ʿAmr b. Abī Sufyān b. Asīd (5) b. Jāriyah (6) al-Thaqafī informed him that Abū Hurayrah said to Kaʿb al-Aḥbār:

“The Messenger of Allah ﷺ said, ‘Every prophet has a supplication which he offers; I, if Allah wills, wish to keep my supplication as an intercession for my ummah on the Day of Resurrection.’”

Kaʿb asked Abū Hurayrah, “Did you hear this from the Messenger of Allah ﷺ?” He replied, “Yes.” Muslim alone narrated this version (7).