وَلَا تَلْبِسُوا الْحَقَّ بِالْبَاطِلِ وَتَكْتُمُوا الْحَقَّ وَأَنْتُمْ تَعْلَمُونَ[Al-Baqarah:42]
Do not cover up the truth with falsehood nor conceal the truth while you know better. (Al-Baqarah: 42).
The Noble Shaykh Saalih al-Fawzaan (may Allah preserve him) stated explaining this verse:
This is another prohibition. Covering up the truth with falsehood. Meaning mixing the truth with falsehood. That which is obligatory is that the truth be distinguished from that which is falsehood. That which is obligatory is that the truth is to be taken and the falsehood is to be abandoned. As for mixing between the truth and falsehood and mixing between Kufr and Eemaan, this is negating the religion of Allah. The obligation of the Ulamaa is that they distinguish between the truth and falsehood. And it was from that which was obligatory upon the Children of Israeel, and they were Ulamaa, that they distinguish between the truth and falsehood. Therefore that which they are upon from Judaism and Christianity after the sending of Muhammad ﷺ, then it is falsehood. As for that which the Messenger ﷺ came with, it is the only truth. Therefore it is not permissible to mix between judaism, Christianity and Islaam. This is mixing between the truth and falsehood. Rather it is to be said: Indeed Islam is the true religion and that which is besides it is falsehood. That's because either it is abrogated by Islam, or either it is distorted and changed from that which Allah has revealed. And there doesn't remain a after the sending of the Messenger ﷺ a religion other than Islam. Allah has said:
إِنَّ الدِّينَ عِنْدَ اللَّهِ الْإِسْلَامُ ۗ وَمَا اخْتَلَفَ الَّذِينَ أُوتُوا الْكِتَابَ إِلَّا مِنْ بَعْدِ مَا جَاءَهُمُ الْعِلْمُ بَغْيًا بَيْنَهُمْ ۗ وَمَنْ يَكْفُرْ بِآيَاتِ اللَّهِ فَإِنَّ اللَّهَ سَرِيعُ الْحِسَابِ['Aali 'Imran:19]
Indeed the religion with Allah is Islam. (Aali 'Imraan:19)and He also stated:
وَمَنْ يَبْتَغِ غَيْرَ الْإِسْلَامِ دِينًا فَلَنْ يُقْبَلَ مِنْهُ وَهُوَ فِي الْآخِرَةِ مِنَ الْخَاسِرِينَ['Aali 'Imran:85]
And whoever desires a relgion other than Islam it will never be accepted from him and in the here after he will be from amongst the losers. (Aali 'Imraan:85).
...and do not conceal the truth while you know better.
It is not permissible for the one who knows the truth to conceal it from the people. Rather it is upon him to clarify it to the people in order that the people can be upon insight. This is the obligation of the Ulamaa, clarifying the truth and not concealing anything from the truth because Allah sent down this knowledge for the people. He didn't send it down for you alone to keep it stored away in your chest leaving the people upon their ignorance and misguidance. Rather it is obligatory upon every 'Aalim to clarify for the people that. which Allah has revealed. Whoever is pleased with it is pleased with it. Whoever dislikes it dislikes it. This is in order that he fulfills his responsibility and in order that Allah benefits whoever He wills the guidance for.