In the BBC radio series 'Incarnations', the episode on Pāṇini is entitled 'Catching the Ocean in a Cow's Hoofprint', which it says is a description of what Pāṇini's work achieved.

Can anyone tell me what the source of this expression specifically in reference to Pāṇini is? Textual/online searches for goṣpada- have not led me very far - but maybe I've been looking for the wrong word?

(In case anyone doesn't know 'Incarnations' and wants to listen to any of the episodes: https://www.bbc.co.uk/programmes/b05rptbv/episodes/downloads)