I say: Its narrators are trustworthy, all of them narrators used by Muslim.

Hammad was corroborated by ‘Abd al-Razzaq (2/39/2402), who narrated it from Ma‘mar and Ibn ‘Uyaynah, from ‘Amr ibn Dinar, from a man of Banu Ghifar, from Abu Basrah, with the same wording.

In another version from him (2400), through Ma‘mar, from Ibn Dinar, from a man whom he named, from Abu Dharr, with the same wording. He did not mention, “from Abu Basrah,” and this is perhaps the correct version, for the man is Abu Basrah, as appears in the narration of Hammad ibn Salamah. Allah knows best.

Moreover, although the hadith is mawquf—stopping at the Companion—it has the force of a hadith attributed to the Prophet, for the reward mentioned in it cannot be stated on the basis of mere opinion, as is apparent—and Allah knows best—especially since its basis has been authentically reported as attributed to the Prophet. Al-Tayalisi (470) said: Sufyan ibn ‘Uyaynah narrated to us from Ibn Abi Najih, from Mujahid, from Abu Dharr, who said:

“I asked the Messenger of Allah, peace and blessings be upon him, about everything, even about smoothing the pebbles. He said: ‘Once.’”

‘Abd al-Razzaq (2404) narrated it likewise.

Its chain of transmission is authentic, if Mujahid heard it from Abu Dharr. For al-Tayalisi said immediately afterward:

“Sufyan said: From al-A‘mash, from Mujahid, from Ibn Abi Layla, from Abu Dharr, from the Prophet, peace and blessings be upon him, with similar wording.”

‘Abd al-Razzaq (2403), Ibn Abi Shaybah, and al-Bazzar (1/275/570) also narrated it with a connected chain, through two routes from Ibn Abi Layla, from ‘Isa ibn ‘Abd al-Rahman ibn Abi Layla, from his father, from Abu Dharr, with the same wording. He added at its end:

“... otherwise, leave it.”

Al-Tahawi (2/183) and Ahmad (5/163) narrated it likewise.