That was 3 decades ago and luckily for us his word was indeed good as gold, but over the years I have almost always needed receipts mainly for my own sense of security. So while making various sizable purchases or payments I learned to achieve my aims by asking for a receipt in such a way that no mistrust was implied -- most commonly by suggesting that I needed it for my personal (or an organization's) financial records:
Now, what is important is not that your whatever reason for requesting a receipt should be extremely credible, but that by expressing your need for a receipt with sincere goodwill, you do indirectly manage to convey to your friend that you absolutely do not mistrust him, while also being extremely careful not to mention trust anywhere in the conversation: personal loan situations are often complicated further by the 'debt of gratitude' element in that your friend was good enough to help you eith a significantly large amount when you really needed the money, and actually trusted you to be able to repay it later; so if your friend appears reluctant to issue a receipt for whatever reason, you might consider not pressing him to do so, and that allows both of you to "save face" inwhile completing the transaction.
