This is one of the classic Buddhist Stories that I heard many times and find it very beneficial.
(Buddhist Monastery @ Inle Lake, Burma)
This version is taken from A New Earth by Eckhart Tolle
Two Zen monks, Tanzan and Ekido, were walking along a country road that had become extremely muddy after heavy rains. Near a village, they came upon a young woman who was trying to cross the road, but the mud was so deep it would have ruined the silk kimono she was wearing. Tanzan at once picked her up and carried her to the other side.
The monks walked on in silence. Five hours later, as they were approaching the lodging temple, Ekido couldn't restrain himself any longer. "Why did you carry that girl across the road?" he asked. "We monks are not supposed to do things like that."
"I put the girl down hours ago," said Tanzan.
"Are you still carrying her?"