Surah Al-Ahzab (The Enemy Alliance), Verse 5

اُدْعُوْهُمْ لِاٰبَآىِٕهِمْ هُوَ اَقْسَطُ عِنْدَ اللّٰهِ فَاِنْ لَّمْ تَعْلَمُوْۤا اٰبَآءَهُمْ فَاِخْوَانُكُمْ فِی الدِّیْنِ وَمَوَالِیْكُمْ وَلَیْسَ عَلَیْكُمْ جُنَاحٌ فِیْمَاۤ اَخْطَاْتُمْ بِهٖ وَلٰكِنْ مَّا تَعَمَّدَتْ قُلُوْبُكُمْ وَكَانَ اللّٰهُ غَفُوْرًا رَّحِیْمًا ۟

Ud'oohum li aabaaa'ihim huwa aqsatu 'indal laah; fa illam ta'lamooo aabaaa'ahum fa ikhwaanukum fid deeni wa mawaaleekum; wa laisa 'alaikum junaahun feemaaa akhtaatum bihee wa laakim maa ta'ammadat quloobukum; wa kaanal laahu Ghafoorar Raheemaa

“Call them by (the names of) their fathers: that is juster in the sight of Allah. But if ye know not their father's (names, call them) your Brothers in faith, or your maulas. But there is no blame on you if ye make a mistake therein: (what counts is) the intention of your hearts: and Allah is Oft- Returning, Most Merciful.”

Quran 33:5 (Yusuf Ali Translation)