Sforno on Leviticus 16:2/ספורנו על ויקרא ט״ז:ב׳

1FOR I APPEAR IN THE CLOUD in this generation to speak to Moshe, but in other generations to call to those prepared for prophecy, as was the case with Shmu'el, as it says (I Sam. 3:3-4), "Shmu'el was sleeping in the temple of Adonai, where the Ark of God was, and Adonai called out to Shmu'el.