The Quranic dua for parents is: 'Rabbi irhamhuma kama rabbayani saghira' — My Lord, have mercy upon them as they brought me up when I was small (Quran 17:24). This dua is recommended to be recited regularly, especially during Hajj and Umrah when duas are readily accepted.
رَبِّ ارْحَمْهُمَا كَمَا رَبَّيَانِي صَغِيرًا
Rabbir-hamhuma kama rabbayani saghira.
Meaning: My Lord, have mercy upon them both, as they brought me up when I was small.
Source: Sahih Muslim #1631This dua is directly from the Quran (Surah Al-Isra, 17:24), making it among the most powerful supplications for parents. Allah commands kindness to parents second only to His own worship. The Prophet said the pleasure of Allah is in the pleasure of the parents, and His anger is in their anger (Sunan al-Tirmidhi 1899).
رَبِّ ارْحَمْهُمَا كَمَا رَبَّيَانِي صَغِيرًا
The Prophet (peace be upon him) said: 'When a person dies, his deeds come to an end except for three: ongoing charity, beneficial knowledge, or a righteous child who prays for him.' This verse from Surah Al-Isra (17:24) is the dua Allah commands for parents.