Source for exclusively learning/seeking Torah from someone whose face is glowing like an angel?

I remember several times coming across a text that asked something along the lines of:
"Who should one seek/learn Torah from?"
or
"How does one know whether to seek/learn Torah from a certain Rabbi?"

And the answer being something along the lines of:
"One who's face is glowing, appearing joyous or as an angel, that's how you tell that he is who you should learn from."

Has someone come across this that could point me to the source?
Thanks in advance.

Answer

This is a Gemara Hagiga (15b):

אם דומה הרב למלאך ה' צבאות - יבקשו תורה מפיהו. ואם לאו - אל יבקשו תורה מפיהו

If the Rav resembles an angels of the Lord of Hosts, seek Torah from his mouth. If not; do not seek Torah from his mouth.