Evangelism described in a cliche – but cliches are often true

A cliche is a now unoriginal phrase that started off as something original and well enough said to be repeated often enough to become a cliche. If you see what I mean. The following brief quotation has a metaphor for evangelism that has entered the less than honoured lists of cliche – but its truth is no less important for its over-exposure:

"Evangelism is witness. It is one beggar telling another beggar where to get food. The Christian does not offer out of his bounty. He has no bounty. He is simply guest at his Master's table and , as evangelist, he calls others too."

D. T. Niles, writing thirty years ago, quoted all over the place but nobody ever footnotes it. Is it oral tradition, or displaced text, or borrowed so often it is now orphaned from the original source. So. Where was it first written? I don't know the answer but want to.