One day Prophet Musa / Moses (pbuh) was passing through a barren
hill. He noticed a pious person busy in prayer sitting in a cave of the
hill. Prophet Musa / Moses (pbuh) felt the urge to meet and talk to the
pious person. Prophet Musa / Moses (pbuh) went near and greeted him. The
pious person asked disinterestedly, "Who are you?" Prophet Musa / Moses
(pbuh) said, "I am Musa!"

The pious person asked, "Are you the Prophet
Musa / Moses (pbuh)?"
Prophet Musa / Moses (pbuh) said, "Yes!"
The pious person said, "Then ask Allah (SWT) to Grant my wish!"
Prophet Musa / Moses (pbuh) asked, "What is it that you want?"
The pious person said, "Since the last one hundred years I am sitting
here praying to Allah (SWT). I don't do anything other than the Prayer.
Ask Allah (SWT), what He will give me for my efforts?"
Prophet Musa / Moses (pbuh) said, "I shall find about it
immediately." He immediately climbed up the hill and called aloud, "O
Sustainer Allah! This person wants to know about the reward for his
prayers! Tell me, what shall I inform him?"
He heard the sound, "O Musa! Tell him, we shall inform him about his
reward tomorrow."
Prophet Musa / Moses (pbuh) went to the pious person and conveyed the
message to him.
The pious person said, "Its fine! Tomorrow is not much of a time!"
The pious person was in the habit of going to a nearby canal early every
morning for bathing and fetching some water for his use. Therefore, the
next morning too he started for the canal but he lost his way and
reached somewhere else. Because of the sun's heat he became very thirsty
and tired. He sat on a lonely boulder and started thinking about his
death. At that time he found another person coming from the other
direction. He waved to the person to come to him. When the person came
nigh, he asked him to help him with some water.
The visiting person said, "Where is any water in this wilderness?
Whatever little I have is only for me."
The pious person started crying. The other person said, "Fine! What
will you give me if I give you a tumbler of water?"
The pious person said, "I don't have anything. I have been busy in
the cave praying for the last one hundred years."
The other person said, "If you agree to transfer to me the Rewards
for your prayers of one hundred years, I shall give you a tumbler of
water."
The pious person thought, if he lived, he could pray for a further
period to get the Reward from Allah (SWT). He said, "I am ready to
transfer to you my reward for the hundred years' of my prayers.
The other person gave him a tumbler full of water and the pious
person returned to his cave.
In the morning Prophet Musa / Moses (pbuh) got a Revelation that the
pious person transferred his hundred years' prayers to another person in
exchange for a tumbler of water. Ask the man to settle the value of the
tumblers of water that he had been drinking during the last hundred
years!
Therefore, Prophet Musa / Moses (pbuh) went to the cave and told to
the person that he had a message for him from Allah (SWT).
The pious person said, "O Prophet Musa / Moses (pbuh)! I have already
sold my hundred years of penance!"
Prophet Musa / Moses (pbuh) said, "Yes! I know. But Allah (SWT) has
said that when the value of one hundred years of prayer is one tumbler
of water, then he must settle the value of the water he had been
drinking over the last hundred years."
When the pious person heard this, he was shocked and shouted, "O
Prophet Musa / Moses (pbuh)! Recommend to Allah (SWT) to forgive my
sins! Allah (SWT) is Beneficent and Merciful!"
Prophet Musa / Moses (pbuh) got the Revelation, "tell the pious
person! Your penitence of this moment pleased us more than your prayers
of a hundred years and we have given to you rewards for a thousand years
of prayers!"
Imam Ali (as) says: "The sin that makes you sad and repentant is more
liked by Allah (SWT) than the good deed which turns you arrogant."