In the folly of youth I one day shouted at my mother who then sat down with a grieved heart in a corner and said, weeping: ‘Hast thou forgotten thy infancy that thou art harsh towards me?’

How sweetly said the old woman to her son
When she saw him overthrow a tiger, and elephant-bodied:
‘If thou hadst remembered the time of thy infancy
How helpless thou wast in my arms
Thou would’st this day not have been harsh
For thou art a lion-like man, and I an old woman.’

Saadi Shirazi

http://www.poemhunter.com/poem/ch-06-on-weakness-and-old-age-story-06/