A man was in debt for 700 Dirhams (silver coins). He came to Hazrat Abdullah Ibn Mubaarak (Rahmatullahi alaih) for assistance.
Hazrat Ibn Mubaarak wrote a letter instructing his manager to give the bearer of the letter seven thousand Dirhams. Instead of seven hundred Dirhams, he mistakenly wrote seven thousand.
When the person who was not aware of the contents, presented the letter to the manager, the manager suspected that Hazrat Ibn Mubaarak had made an error. He asked the man what his need was. He replied 700 Dirhams. The manager told him to wait.
Meanwhile he wrote to Ibn Mubaarak informing him that the man’s need was only 700 Dirhams, hence he sought clarification.
Hazrat Ibn Mubaarak (Rahmatullahi alaih) wrote back: “On receipt of my letter, give the man fourteen thousand Dirhams.”
Although he realized the error, he did no retract the amount. Instead, his generosity dictated that the amount to be given should be doubled.
Source: Subulas Salaam, page 54)