Hadith.3831 - Samaah asked him about purchasing milk while it is still in the udders.
Imam (as) said: "No, unless he milks some of it into a small vessel (sukurjah) for you, and then you say, 'I purchase from you this milk that is in the vessel and what is in its udders for a specified price.' If there is nothing in the udders, then the sale applies to what is in the vessel."