Albert Barnes Commentary 1 Kings 20:10

"And Ben-hadad sent unto him, and said, The gods do so unto me, and more also, if the dust of Samaria shall suffice for handfuls for all the people that follow me." — 1 Kings 20:10 (ASV)

If the dust of Samaria will suffice for handfuls... — In its general sense, this phrase is undoubtedly a boast that the number of Ben-hadad’s troops was so great as to make resistance vain and foolish. We can compare it to the saying of the Trachinian at Thermopylae that the Persian arrows would darken the sun. The probable, exact meaning is: “When your town is reduced to ruins, as it will be if you resist, the entire heap will not be enough to provide a handful of dust for each soldier of my army, because it is so large.” The message contained a threat as well as a boast.