It is narrated from Sufyan (may Allah have mercy on him), Imam Zuhri (may Allah have mercy on him) said: I used to think that I had completed knowledge, but when I kept the company of Ubaidullah (bin Abdullah bin Mas'ud), I realized that I was only in one of the many valleys or ravines of knowledge (i.e., compared to him, my knowledge was very little).
Hadith Takhrijاس روایت کی سند صحیح ہے۔ دیکھئے: [تاريخ أبى زرعة 1395]
Brief Explanation
(Explanation of Ahadith 626 to 649) From all these traditions, the esteem and status of scholars, the importance and virtue of visiting them, and the necessity of scholarly discussion of ahadith and memorizing principles are established. Furthermore, it is proven that memorizing and repeating ahadith does not fall under idle talk (samar) which has been prohibited in the ahadith, and that scholarly discussion is better than spending the entire night in voluntary prayer (tahajjud).