It is when Lara first becomes involved with Komarovsky. She goes to a church and speaks with a priest about forgiveness. I believe the priest is Burton. He has on very dark make-up and long hair but the voice is unmistakable. And I have a remarkable ear for identifying voices. The dialog lasts no more than a minute or two.
I was just watching Dr Zhivago and I am almost certain that Richard Burton has a brief cameo. Is there any place I can search to confirm this? I have looked in the cast listings on Wiki, IMBD, TCM and Rotten Tomatoes