[If] he was sitting in a boat or a wagon, or on a raft, he should concentrate his thoughts toward the Chamber of the Holy of Holies [while praying].

R’ Elazar ben Azaryah says: The Mussaf Prayer is only [recited] with an assembly of the town. But the Sages say: [It is recited] with an assembly of the town and without an as-sembly of the town. R’ Yehudah says in his name: Any place where there is an assembly of the town, an individual is exempt from the Mussaf Prayer.