One who causes the death of an animal without intent

A message was received by the program from Iraq as well, stating: I am the listener (M. R.) from al-Azamiyyah, Baghdad. I listen to your program daily and thank you for it for the benefit it offers to everyone. Therefore, I am sending you these questions and hope that you will answer them and not neglect them.
The first question is that forty years ago, I was busy with household matters, so I told my son to lock the chickens in the oven so that I could get rid of their annoyance, because I was working and forgot that the oven was hot, because I had baked in it the day before. The chickens died, and I did not intend it. Do I have a sin upon me, and do I have an expiation? Please inform us, may Allah reward you with good.
Answer: You owe nothing as long as you did not intentionally kill it without right in this manner, but rather it was an oversight and a mistake on your part. You owe nothing, and praise be to Allah. Yes.
The presenter: May Allah reward you.