'What is the origin of water?' 'That world (heaven),' he replied. 'And what is the origin of that world?'— He replied: 'Let no man carry the Sâman beyond the world of svarga (heaven). We place (recognise) the Sâman in the world of svarga, for the Sâman is extolled as svarga (heaven).'
In plain words: Dalbhya said water comes from heaven. When asked where heaven comes from, he said the questioning should stop there, because the chant belongs in heaven.