וַיְהִ֕י כַּאֲשֶׁ֥ר שָׁמַ֛ע עֶ֥בֶד אַבְרָהָ֖ם אֶת־דִּבְרֵיהֶ֑ם וַיִּשְׁתַּ֥חוּ אַ֖רְצָה לַֽיהוָֽה׃
Le serviteur d’Abraham, ayant entendu leurs paroles, se prosterna à terre en l’honneur de l’Éternel;
Sforno
וישתחו ישראל, to give thanks to His Creator for enabling him to exact this promise from his son.. We find that Eliezer, after hearing that Rivkah’s family agreed that he take Rivkah as a wife for Yitzchok, reacted in the very same fashion in 24,52 וישתחו ארצה לה', “he prostrated himself on the earth to G’d.”
Rashi
ויאמר אחיה ואמה AND HER BROTHER AND HER MOTHER SAID —But where was Bethuel? He wished to prevent the marriage therefore an angel came and killed him (Genesis Rabbah 60:12).