Which Scottish writer penned this phrase - Beware a tongue smoothly hung?

The phrase "Beware a tongue smoothly hung" is attributed to Sir Walter Scott, a prominent Scottish writer.

While the exact source of the quote is debated, it is widely believed to originate from his historical novel, "Rob Roy" (1817). In the novel, the character of "Bailie Nicol Jarvie" utters a similar sentiment, warning about the danger of flattery.