תּלמוד אויף דברים 9:9

One verse says, "And I sat [va'eshev] on the mountain" (Deuteronomy 9:9), and another verse says, "And I stood on the mountain"(Deuteronomy 10:10): Rav says: He [Moses] stood when he learned and sat while he repeated [what he had learned]. R. Hanina said: He was neither sitting nor standing, but stooping. R. Yohanan said: Sitting here means only "staying", as it says, "And you stayed [teshvu] in Kadesh many days" (Deuteronomy 1:46). Rava said: The easy things [he learned] standing and the hard ones sitting