Ibn Abi Uwais (rahimahullah) mentions that he heard Imaam Maalik (rahimahullah) say, “This knowledge is (your) Deen. Therefore, be cautious regarding those from whom you take your Deen. I found seventy people narrating the Ahaadith of Rasulullah (sallallahu ‘alaihi wasallam) at these pillars of the musjid.” Saying this, Imaam Maalik (rahimahullah) gestured towards the pillars of Musjid Nabawi (sallallahu ‘alaihi wasallam). Imaam Maalik (rahimahullah) continued, “However, I did not narrate any Hadith from them, even though each of them was such that if he had to be entrusted with the Bayt-ul-Maal (public treasury), he would be completely honest and trustworthy. The reason that I did not narrate Hadith from them is that they were not sufficiently qualified in the field of Hadith.”
Imaam Maalik (rahimahullah) has also mentioned, “I saw Hazrat Ayyoob Sakhtiyaani (rahimahullah) in Makkah Mukarramah during two journeys of Haj, yet I did not narrate Hadith from him. During the third journey for Haj, I saw him seated in the vicinity of the Zam-Zam well. Whenever the blessed name of Rasulullah (sallallahu ‘alaihi wasallam) was taken in his presence, he would cry so profusely that I would pity him. When I saw this to be his condition, I narrated Hadith from him.
(Ad-Deebaaj-ul-Muzahhab 1/100-101)