Addressing one's parents with titles of respect
Q: I wanted to know, what is the correct Sunnah way to address your Mum and Dad? What did Nabi (Sallallahu Alaihi Wasallam's) blessed children address him and Sayyidina Khadijah (Radiyallahu Anha) by? Was it Abba and Amma? Or Abu and Ummi? Or any other titles?