Rashi on Numbers 32:25/רש"י על במדבר ל״ב:כ״ה

1ויאמר בני גד AND THE CHILDREN OF GAD SAID, all of them as one man (ויאמר is the singular form of the verb, whilst the subject בגי גד is the plural; cf. Rashi on Exodus 19:2 s. v.).