This is an interesting account of a preacher who was converted in his pulpit while preaching. It is from the book, From Death To Life: Twenty Years Of My Ministry by Rev. William Haslam, 1886

“So I went up into the pulpit and gave out my text. I took it from the gospel of the day—”What think ye of Christ?” (Matt. 22:42).

As I went on to explain the passage, I saw that the Pharisees and scribes did not know that Christ was the Son of God, or that He was come to save them. They were looking for a king, the son of David, to reign over them as they were. Something was telling me, all the time, “You are no better than the Pharisees yourself-you do not believe that He is the Son of God, and that He is come to save you, any more than they did.” I do not remember all I said, but I felt a wonderful light and joy coming into my soul, and I was beginning to see what the Pharisees did not.

Whether it was something in my words, or my manner, or my look, I know not; but all of a sudden a local preacher, who happened to be in the congregation, stood up, and putting up his arms, shouted out in a Cornish manner, “The parson is converted! The parson is converted! Hallelujah!” and in another moment his voice was lost in the shouts and praises of three or four hundred of the congregation. Instead of rebuking this extraordinary “brawling,” as I should have done in a former time, I joined in the outburst of praise; and to make it more orderly, I gave out the Doxology—”Praise God, from whom all blessings flow”—and the people sang it with heart and voice, over and over again. My Churchmen were dismayed, and many of them fled precipitately from the place. Still the voice of praise went on, and was swelled by numbers of passers-by, who came into the church, greatly surprised to hear and see what was going on.

When this subsided, I found at least twenty people crying for mercy, whose voices had not been heard in the excitement and noise of thanksgiving. They all professed to find peace and joy in believing. Amongst this number there were three from my own house; and we returned home praising God.

The news spread in all directions that “the parson was converted,” and that by his own sermon, in his own pulpit to. The church would not hold the crowds who came in the evening. I cannot exactly remember what I preached about on that occasion; but one thing I said was, “that if I had died last week I should have been lost for ever.” I felt it was true. So clear and vivid was the conviction through which I had passed, and so distinct was the light into which the Lord had brought me, that I knew and was sure that He had “brought me up out of an horrible pit, out of the miry clay, and set my feet upon a Rock, and put a new song into my mouth” (Ps. 40). He had “quickened” me, who was before “dead in trespasses and sins,” (Eph. 2:1).”

http://www.gutenberg.org/cache/epub/14578/pg14578.html