hide one's light under a bushel - Phrases/Idioms
The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 2003, 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Show extreme modesty, as in Even after Paul won the scholarship be went on hiding his light under a bushel. This expression, which does not necessarily express approval of this behavior, has its origin in the New Testament (Matthew 5:15): “Neither do men light a candle, and put it under a bushel, but on a candlestick.” [Early 1600s]