“I once said to abu al-Hassan ‘Alayhi al-Salam, ‘I may buy certain things in the presence of my father and I see certain things in him that make me depressed.’ He (the Imam) said, ‘Avoid buying in his presence. When you have a right on a man say to him, “Write down, ‘So and so has written in his handwriting, assigning Allah as witness upon himself and Allah is sufficient witness.’” He will certainly pay in his life time or after his death.’”