וַיָּבֹ֥אוּ בְנֵֽי־גָ֖ד וּבְנֵ֣י רְאוּבֵ֑ן וַיֹּאמְר֤וּ אֶל־מֹשֶׁה֙ וְאֶל־אֶלְעָזָ֣ר הַכֹּהֵ֔ן וְאֶל־נְשִׂיאֵ֥י הָעֵדָ֖ה לֵאמֹֽר׃
迦得的子孫和流便的子孫來到摩西、以利亞撒祭司和會眾的首領那裡，對他們說：
Shenei Luchot HaBerit
As to the reason why Gad is singled out here and no mention is made of the other one and a half tribes who were a party to the same agreement, I think it may well be that since the Torah had reported the tribe of Gad as the first to demand its share of the land on the East bank, this tribe had been more suspect than its partners as perhaps unwilling to share the problems of the other tribes. When even this tribe assumed a greater burden than had been required, the Torah rewarded it by mentioning it first always.