strike dumb

She saw Feral, stricken dumb, his mouth actually agape.

Suddenly as they talked they were stricken dumb, frozen as it were to listening stones.

He even seemed for a moment to be stricken dumb with surprise and emotion.

From without we had heard the gay clamour of voices, but with our unexpected entrance all seemed stricken dumb.

And she turned to Henrietta, who, stricken dumb by the scene, recognised too late the trap into which she had fallen.