Reference for Berakhot 92:7

אמר ליה וכי בעי אשתעויי בהדיה מתריץ תרוצי ויתיב ומשתעי בהדיה א"ל שאני פרסאי דמחוי ליה במחוג

Rab Sheshet said to him, "But should the chief guest wish to converse with him [who is above him], he would have to straighten himself and sit up to do so!" The Exilarch replied, "It is otherwise with the Persians, because he would communicate with him by gesture."

Jastrow