Friendship

There were two friends walking in the desert and during their walk one of them slapped the other friend he suffered.but he did not say any thing but he wrote on the sand "today my best friend slapped my face" They continued to walk,They found an oasis they decided to take a bath in the water but who was slapped and suffered from his friend was drowning his friend saved him from drowning the other friend wrote on the a stone "today my friend saved my life"
his friend asked his when I slapped you wrote on sand and when I saved you from drowning you wrote on stone. why ?
he smiled and replied when friends hurt us we should write down what happened on the sand so winds can erase it for tolerance and forgiveness,but when friends make good things for us we must write it on stone to stay in the memory of the heart and winds will not erase it.