Our parents have sacrificed so much to raise us. We can never repay them for their kindness. However, we can do our best to honour them and treat them well.
Allah s.w.t. says in the Quran:
Your Lord has decreed that you worship none but Him and that you be kind to parents. Whether one or both of them attain old age in your life, say not to them a word of contempt, nor repel them, but address them in terms of honour
(Surah Al-Isra, 17:23)
One of the best things that you can do is to constantly make sincere dua for them, even if they are no longer with us. The Prophet s.a.w. encouraged us to keep praying for our parents. Indeed, prayers will continue to benefit them.
When a person dies, his deeds come to an end, except for three: A continuous charity, knowledge that others benefited from, and a pious son who (continues to) pray for him
There are so many kinds of Dua that we can pray for our parents. It can even be any prayer that is voiced deep from the heart. Truly, Allah will hear even our slightest cry. Here are some prayers from the Quran to be made for our parents:
رَبَّنَا اغْفِرْ لِي وَلِوَالِدَيَّ وَلِلْمُؤْمِنِينَ يَوْمَ يَقُومُ الْحِسَابُ
Rabbana-ghfirlī wa liwālidayya wa lilmu'minīna yauma yaqūmul-hisāb
Our Lord! Forgive me, my parents, and the believers on the Day when the judgment will come to pass.
(Surah Ibrahim, 14:41)
رَّبِّ ارْحَمْهُمَا كَمَا رَبَّيَانِي صَغِيرًا
Rabbi irhamhuma kama rabbayanee sagheera
“My Lord! Be merciful to them as they raised me when I was young.”
(Surah Al-Isra’ 17:24)
رَّبِّ اغْفِرْ لِي وَلِوَالِدَيَّ وَلِمَن دَخَلَ بَيْتِيَ مُؤْمِنًا وَلِلْمُؤْمِنِينَ وَٱلْمُؤْمِنَٰتِ
Rabbana-ghfirlī wa liwālidayya wa liman dakhola baytī mu'minan wa-lilmu'minīna wal-mu'mināt
My Lord! Forgive me, my parents, and whoever enters my house in faith, and all believing men and women
(Surah Nuh, 71:28)
رَبِّ أَوْزِعْنِي أَنْ أَشْكُرَ نِعْمَتَكَ الَّتِي أَنْعَمْتَ عَلَيَّ وَعَلَىٰ وَالِدَيَّ وَأَنْ أَعْمَلَ صَالِحًا تَرْضَاهُ وَأَدْخِلْنِي بِرَحْمَتِكَ فِي عِبَادِكَ الصَّالِحِينَ
Rabbi awzi'nī an asykura ni'matikal-latī an'amta 'alayya wa 'ala wālidayya wa an a'mala salihan tardhāhu wa adkhilnī birahmatika fī 'ibādikas-soliheen
My Lord, inspire me to (always) be thankful for the blessings You have granted me and my parents, and to do good deeds that please You; admit me by Your grace into the ranks of Your righteous servants
(Surah An-Naml, 27:19)
Check out Muslim.Sg's dua collection!