Pen

If a person,

1. rising at early dawn and 
2. taking with him a quantity of water and 
3. a few blades of Kusa grass, 

proceeds into a cow-pen and arriving there washes a cow's horns by sprinkling thereon that water with those blades of Kusa grass and then causes the water to drip down on his own head, he is regarded, in consequence of such a bath, as one that has performed his ablutions in all the sacred waters that the wise have heard to exist in the three worlds

http://www.sacred-texts.com/hin/m13/m13b095.htm