Mahavagga, Khandaka 2, Chapter 6

Now the Bhikkhus thought: 'The Blessed One has prescribed that completeness (of the assembled fraternity) is to extend as far as one residence^[1]. Now how far does one residence extend?'

They told this thing to the Blessed One.

“I prescribe, O Bhikkhus; that you determine a boundary. And it ought to be determined, O Bhikkus, in this way: First the landmarks are to be proclaimed: a landmark consisting in a mountain, in a rock, in a wood, in a tree, in a path, in an anthill, in a river, in a piece of water. The landmarks having been proclaimed, let a learned, competent Bhikkhu proclaim the following ñatti before the Saṃgha: "Let the Saṃgha, reverend Sirs, hear me. If the Saṃgha is ready, let the Saṃgha, as the landmarks have been proclaimed all around, by these land marks determine the boundary for common residence and communion of Uposatha. This is the ñatti. Let the Saṃgha, reverend Sirs, hear me. The Saṃgha determines the boundary (&c., as above). Thus I understand."”