Imaam Ibnul Qayyim (rahimahullaah) reported in I’laam Al-Muwaqqi’een 2/185 that Ibn Mas’ood (radiyallaahu-anhu) said, “Whoever has knowledge, then let him speak with it. And whoever does not have knowledge, then let him say, ‘Allaah knows best’, for indeed Allaah said to His Prophet:

[قُلْ مَا أَسْأَلُكُمْ عَلَيْهِ مِنْ أَجْرٍ وَمَا أَنَا مِنَ الْمُتَكَلِّفِينَ  – Say (O Muhammad): “No wage do I ask of you for this (the Qur’an), nor am I one of the Mutakallifun (those who pretend and fabricate things which do not exist). [Surah Saad. Ayah 86]