Surah Luqman (Luqman), Verse 13

وَاِذْ قَالَ لُقْمٰنُ لِابْنِهٖ وَهُوَ یَعِظُهٗ یٰبُنَیَّ لَا تُشْرِكْ بِاللّٰهِ اِنَّ الشِّرْكَ لَظُلْمٌ عَظِیْمٌ ۟

Wa iz qaala luqmaanu libnihee wa huwa ya'izuhoo ya bunaiya laa tushrik billaah; innash shirka lazulmun 'azeem

“Behold, Luqman said to his son by way of instruction: "O my son! join not in worship (others) with Allah: for false worship is indeed the highest wrong-doing."”

Quran 31:13 (Yusuf Ali Translation)