Do it right when you write, speak, or make someone write.
If you make a deal that’s not paid right away, and the payment will happen later, write it down.
Someone who knows how to write should write it truthfully.
Don’t hold back from writing what is fair just because it’s not convenient.
Write as Allah has taught you.
If you're the one owing money, say clearly what the agreement is so it can be written.
Be mindful of Allah when doing this.
Also, when you speak, be fair, even if it involves someone close to you.
And keep your promises to Allah.
(from Syajaratul Ma‘arif, Syaikh al-‘Izz bin Abdus Salam)