Surah Al-Isra' (The Night Journey), Verse 23

وَقَضٰی رَبُّكَ اَلَّا تَعْبُدُوْۤا اِلَّاۤ اِیَّاهُ وَبِالْوَالِدَیْنِ اِحْسَانًا اِمَّا یَبْلُغَنَّ عِنْدَكَ الْكِبَرَ اَحَدُهُمَاۤ اَوْ كِلٰهُمَا فَلَا تَقُلْ لَّهُمَاۤ اُفٍّ وَّلَا تَنْهَرْهُمَا وَقُلْ لَّهُمَا قَوْلًا كَرِیْمًا ۟

Wa qadaa Rabbuka allaa ta'budooo illaaa iyyaahu wa bilwaalidaini ihsaanaa; immaa yablughanna 'indakal kibara ahaduhumaaa aw kilaahumaa falaa taqul lahumaaa uffinw wa laa tanharhumaa wa qullahumaa qawlan kareemaa

“Thy Lord hath decreed that ye worship none but Him, and that ye be kind to parents. Whether one or both of them attain old age in thy life, say not to them a word of contempt, nor repel them, but address them in terms of honour.”

Quran 17:23 (Yusuf Ali Translation)