A.T. Robertson Commentary Mark 9:34

"But they held their peace: for they had disputed one with another on the way, who [was] the greatest." — Mark 9:34 (ASV)

But they held their peace (Hο δε εσιωπων). Imperfect tense. Put thus to them, they felt ashamed that the Master had discovered their jealous rivalry. It was not a mere abstract query, as they put it to Jesus, but it was a canker in their hearts.