He wrote a receipt for her for money that she would be entitled to in the event of abuse or mistreatment
Obliging the husband to pay money to his wife if he mistreats her or abuses her, or obliging the wife likewise, is not binding and in fact is not prescribed in sharia at all. Determining the degree of a punishment is not up to people, and imposing payment of money as a punishment -- even if it is permissible -- is up to the judge. Moreover writing a receipt to this effect is a kind of lying, because neither of them has received anything from the other in that regard.
Based on that, these receipts should be disposed of and should not be relied upon at all.
Each of the two spouses must treat the other well, and adhere to that which Allaah has commanded of kind and decent treatment. Allaah, may He be exalted, says (interpretation of the meaning):
“and live with them honourably”
“And they (women) have rights (over their husbands as regards living expenses) similar (to those of their husbands) over them (as regards obedience and respect) to what is reasonable, but men have a degree (of responsibility) over them”
And Allaah knows best.