A man in Tihad jail receives a letter from his wife:
"Dear Husband, I have decided to plant some onion in the back garden. When is the best time to plant them?"
The prisoner, knowing that the prison guards read all mail, replied in a letter:
"Dear Wife, whatever you do, do not touch the back garden. That is where I hid all the money."
A week or so later, he received another letter from his wife:
"Dear Husband, You wouldn't believe what happened, some men came with shovels to the house, and dug up all the back garden."
The prisoner wrote another letter back:
"Dear wife, now is the best time to plant the onion."