Help Tracking Down a Possible Carey Quote

A reader of this blog has submitted a question which we don't know the answer. His query is posted below. Please respond in the comments if you know the source of the quote that he is trying to track down.

In my reading I came across a statement of Carey's that struck me, but I only made a mental note to return to it later. Now  I cannot find it for the life of me!  Writing back to England I think, he addressed the question of what kind of men should be sent out to the mission field. He said, do not send men who will sit comfortably waiting for sinners to come to them. But, send men who will be out daily among the people seeking the lost. Often on horseback. Otherwise the work will die under their care. Do you know where I can find this? I have looked for hours unsuccessfully.