Horrible joke

"The wise old Mother Superior was dying.
The nuns gathered around her bed, trying to make her comfortable. They gave
her some warm milk to drink, but she refused it. Then one nun took the glass
back to the kitchen. Remembering a bottle of whiskey received as a gift the
previous Christmas, she opened it and poured a generous amount into the warm
milk.
Back at Mother Superior's bed, she held the glass to her lips. Mother drank
a little, then a little more, then before they knew it, she had drunk the
whole glass down to the last drop.
Mother, Mother' the nuns cried, 'Give us some wisdom before you die!'
She raised herself up in bed with a pious look on her face and pointing out
the window, she said,
'Don't sell that cow!'"