Abu Bakr al-Bayhaqi: Hafiz, Hadith Master
Abu Hatim al-Razi: He has some mistakes in his narrations from Basra, but he is generally reliable
Abu Hatim ibn Hibban al-Busti: He was a jurist, pious, حافظ (preserver of knowledge), and righteous
Abu Abd Allah al-Hakim al-Naysaburi: Trustworthy, Reliable
Abu Muhammad ibn Hazm al-Zahiri: Trustworthy
Ahmad ibn Hanbal: You will not find anyone who studied with Muammar who wasn't surpassed by him in seeking knowledge, he was the most knowledgeable of his time
Ahmad ibn Shuayb al-Nasai: Trustworthy, Reliable
Ahmad ibn Salih al-Jili: Trustworthy, righteous man
Ibn Hajar al-'Asqalani: Trustworthy, Upright, Excellent, except that there are some issues in his narrations from Thabit, al-A'mash, Hisham ibn Urwa, and Asim ibn Abi al-Najud, as well as in what he narrated in Basra. He once said: He is one of the most knowledgeable people in Maghazi (Prophet's battles) and all the Imams relied on him
al-Daraqutni: I don't know anyone more noble than Muammar. And once: Trustworthy
al-Dhahabi: One of the prominent trustworthy narrators, he has some known mistakes, but they are overlooked due to his vast knowledge
Abd al-Malik ibn Abd al-Aziz ibn Jurayj: There was no one left from his time more knowledgeable than him
Amr ibn Ali al-Fallas: One of the most truthful people
Muhammad ibn Idris al-Shafi'i: He praised him
Authors of Tahdhib al-Tahdhib: Trustworthy, Upright, the Imams have declared him trustworthy, and he is one of the mountains of knowledge, and there is no doubt that he has very few mistakes considering his vast knowledge
Yahya ibn Ma'in: Trustworthy, and he is one of those I consider trustworthy in Maghazi
Yaqub ibn Shaybah al-Suddusi: Trustworthy, righteous, upright, narrated from al-Zuhri