On the authority of Abu Musa, who said: The Messenger of Allah, peace and blessings be upon him, was asked: "Which of the Muslims is best?" He said: "The one from whose tongue and hand the Muslims are safe." (1)

This is a sound (sahih) and unique (gharib) hadith among the narrations of Abu Musa.

2671 - Ahmad ibn Mani' narrated to us, Muhammad ibn al-Hasan ibn Abi Yazid al-Hamdani narrated to us, from Thawr ibn Yazid, from Khalid ibn Ma'dan, from Mu'adh ibn Jabal, who said: The Messenger of Allah, peace and blessings be upon him, said: "Whoever reproaches his brother for a sin will not die until he commits it himself." (2)

Ahmad said: They said: "For a sin from which he has already repented."

This is a good (hasan) and unique (gharib) hadith, but its chain of transmission is not continuous. Khalid ibn Ma'dan did not meet Mu'adh ibn Jabal. It is narrated from Khalid ibn Ma'dan that he met seventy of the Companions of the Prophet, peace and blessings be upon him, and Mu'adh ibn Jabal died during the caliphate of 'Umar ibn al-Khattab. Khalid ibn Ma'dan narrated from more than one of Mu'adh's companions, from Mu'adh, more than one hadith.

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(1) Sound (sahih). Narrated by al-Bukhari (11), Muslim (42), and al-Nasa'i 8/106. It will be repeated as number (2628).
(2) Its chain is very weak, rather nearly fabricated (shabih mawdu'). Indeed, Khalid ibn Ma'dan did not hear from Mu'adh, and Muhammad ibn al-Hasan ibn Abi Yazid al-Hamdani is a liar. Ibn al-Jawzi said in "al-Mawdu'at" after citing it, 3/82: This hadith is not authentic from the Messenger of Allah, peace and blessings be upon him, and the one accused of fabricating it is Muhammad ibn al-Hasan. Ahmad ibn Hanbal said: I do not think he is worth anything. Yahya said: He was a liar. Al-Nasa'i said: His hadith is abandoned (matruk al-hadith). Al-Daraqutni said: He is nothing. It was also cited by Ibn 'Adi 6/2181, and al-Khatib in his "Tarikh" 2/339-340.