Grading: This hadith is "sahih li-ghayrihi" (authentic due to supporting reports), but this chain is weak because of the "jahalah" (unknown status) of Khalid bin Wahban.
Technical note / Defect ('illah): Here there is also an "inqita'" (break) in the chain between Khalid and Mutarrif, because in the versions of other imams Abu al-Jahm (Sulayman bin al-Jahm) appears as an intermediary between them, and he is the only one to narrate from Khalid bin Wahban; Mutarrif here is Mutarrif bin Tarif al-Harithi.
Reference / Source: Imam Ahmad narrated it in 35/ (21560 - 21562) and Abu Dawud in (4758) through various routes from Mutarrif, from Abu al-Jahm, from Khalid bin Wahban.

Corroborating chains and supporting reports: The next two hadiths, of Ibn 'Umar and al-Harith al-Ash'ari (may Allah be pleased with them), with the same wording, are supporting reports (shawahid) for it, and both of them are "sahih".

Details of the narration: There are several other hadiths in this chapter with the same meaning, which can be seen under the hadith of Ibn 'Umar in "Musnad Ahmad" 9/ (5386).

Note / Clarification: "Qid shibr" means the measure of one hand-span.

Note / Clarification: Regarding the word "al-ribqah", Ibn al-Athir says in "al-Nihayah": "al-ribqah" originally refers to a loop in a rope that is placed on the neck or foreleg of an animal to restrain it. Here it is used metaphorically for Islam, meaning the loops or bonds of Islam by which a Muslim binds himself, that is, the limits, rulings, commands and prohibitions of Islam.