Grading: Its chain is very weak (da'if jiddan).
Technical note / Defect ('illah): The narrator al-Rabi' bin Badr (Ibn 'Amr bin Jarad) is matruk, and his father and grandfather are both majhul.

Reference / Source: Ibn Majah (972) recorded it from Hisham bin 'Ammar, from al-Rabi' bin Badr, with this chain. See the rest of its takhrij there.

Corroborating chains and supporting reports: On this topic there is a report from Samurah (may Allah be pleased with him) in al-Ruyani's "Musnad" (835); its chain contains Isma'il bin Muslim al-Makki, who is weak. Its wording is: "Two or more are a congregation."
Technical note / Defect ('illah): In our view this wording is a mistake; the correct wording is what came in the two narrations with him (al-Ruyani) at (788) and (827): "When you are two, let one of you stand beside his companion, and when you are three, let one of you stand in front (as imam)."

Corroborating chains and supporting reports: From 'Abd Allah bin 'Amr (may Allah be pleased with them both) in al-Daraqutni (1088), but its chain contains 'Uthman bin 'Abd al-Rahman bin 'Umar bin Sa'd bin Abi Waqqas, who is matruk al-hadith.

Corroborating chains and supporting reports: From al-Hakam bin 'Umayr al-Thumali with Ibn Sa'd (9/418), Ibn Abi Khaythamah in the second part of "al-Tarikh al-Kabir" (1/150), Abu al-Qasim al-Baghawi in "al-Sahabah" (482), Ibn 'Adi (5/250) and Ibn 'Abd al-Barr in "al-Tamhid" (14/138).
Technical note / Defect ('illah): Its chain is "musalsal bi-l-du'afa'" (a continuous series of weak narrators).

Corroborating chains and supporting reports: From Abu Umamah (may Allah be pleased with him) with al-Tabarani in "al-Mu'jam al-Awsat" (6624) and "Musnad al-Shamiyyin" (877), and Ibn 'Adi in "al-Kamil" (6/315). It contains Maslamah bin 'Ali al-Husani, who is matruk.
Details of the narration: It has another route with different wording in "Musnad Ahmad" (36/22189), and its chain is also very weak.

Corroborating chains and supporting reports: From Anas bin Malik (may Allah be pleased with him) with Ibn 'Adi (3/366) and al-Bayhaqi (3/69); it contains Sa'id bin Zarbi, who is weak and munkar al-hadith.

Reference / Source: Ahmad (36/22315) recorded it as mursal through the route of Thawr bin Yazid, from al-Walid bin Abi Malik, attributing it to the Prophet (marfu').
Grading: Its narrators are thiqah.

Reference / Source: Abu Dawud recorded it as mursal in "al-Marasil" (26) through the route of al-Qasim Abu 'Abd al-Rahman, attributing it to the Prophet.
Grading: Its narrators are thiqah.

Reference / Source: Abu Dawud also recorded it as mursal in "al-Marasil" (26) through the route of Makhul, attributing it to the Prophet.
Grading: Its narrators are also thiqah.

Grading: The hadith is sahih, and this chain is good (jayyid) because of al-Husayn bin Hafs, and he has been corroborated.

Reference / Source: Ahmad (6/3691 and 7/4195), al-Bukhari (6742), Ibn Majah (2721), al-Tirmidhi (2093) and al-Nasa'i (6294) recorded it through various routes from Sufyan al-Thawri, with this chain.

Reference / Source: Ahmad (7/4073, 4420), al-Bukhari (6736), Abu Dawud (2890), al-Nasa'i (6295, 6296) and Ibn Hibban (6034) recorded it through various routes from Abu Qays.