Rashi, on Isa 6:3

“And they cried one to another, and said: Holy, holy, holy, the Lord God of hosts, all the earth is full of his glory.”

“And one called to the other They would take permission from one another so that one would not commence before [his fellows] and be guilty of [a sin punishable by] burning, unless they all commenced simultaneously. This is what was established in [the blessing commencing:] “...Who formed light,” “the declaration of holiness, they all respond as one...” This is a Midrash Aggadah of the account of the Merkavah. And so did Jonathan render this. Holy, holy, holy Three times, as the Targum renders.”

Imported from an open dataset — not yet checked against the printed edition.