Piety:

Sheikh ‘Abdul ‘Azeez Muhaddith Dehlawi (rahimahullah) has mentioned that one of the outstanding qualities of Imaam Muslim (rahimahullah) is that throughout his life, he never engaged in the gheebah (backbiting) of any person, nor did he physically or verbally abuse any person. (Bustaan-ul-Muhadditheen [English] pg. 81)

Rank in Hadith:

Imaam Abu Ya’qoob, Ishaaq bin Mansoor Al-Kawsaj (rahimahullah), was among the Ustaads of Imaam Muslim (rahimahullah). It is reported that on one occasion, he addressed Imaam Muslim (rahimahullah) and said, “We will continue to receive goodness and benefit so long as Allah Ta‘ala keeps you alive among the people.”

Ahmed bin Salamah (rahimahullah) mentions, “I saw Imaam Abu Zur’ah (rahimahullah) and Imaam Abu Haatim (rahimahullah) prefer Imaam Muslim to many other great Muhadditheen of his era in the field of authenticating Ahaadith.”

Imaam Ishaaq bin Raahwayh (rahimahullah) was also among the Ustaads of Imaam Muslim (rahimahullah). He once mentioned the following, marveling at the expertise of Imaam Muslim (rahimahullah), “What a great person he is!”

Muhammed bin Bashaar (rahimahullah) once said, “There are four Muhadditheen who are regarded as the Muhadditheen of the world (in their era); Imaam Abu Zur’ah (rahimahullah) in the city of Rayy, Imaam Muslim (rahimahullah) in the city of Naisapoor, Imaam ‘Abdullah Daarami (rahimahullah) in the city of Samarqand, and Imaam Muhammed bin Ismaa’eel Bukhaari (rahimahullah) in the city of Bukhaara.”

(Siyar A’laamin Nubalaa 12/557-564)