Bismillahirrahmanirrahim
 
Quranic Dua to ask Mercy for the parents
———-
رَّبِّ ارْحَمْهُمَا كَمَا رَبَّيَانِي صَغِيرًا
“My Lord! Bestow on them ( parents) Your Mercy as they did bring me up when I was young.” 
Surah Al-Isra (17), Verse 23-24