What is the authenticity of the Hadith that refers to the beautification of the Qur’an with voices and the use of musical scales (maqamat), along with the warning about a generation that sings the Qur’an, and what are the principles that must be followed when reciting the Qur’an to avoid sin, and is the use of maqamat by prominent reciters to embody meanings correct, and what is the ruling on the prayer led by an Imam who sings the recitation and does not adhere to Tajwid or linguistic rules?

The Hadith you referred to in your question is the Hadith of Hudhaifah, narrated by Al-Bayhaqi and Al-Tabarani, in which the Prophet (peace be upon him) said: "Recite the Quran with the tunes of the Arabs and their voices. Beware of the tunes of the people of passion and the tunes of the People of the Two Books. After me, there will come people who will recite the Quran like singing and wailing. It will not go beyond their throats. Their hearts will be infatuated, and so will be the hearts of those who are pleased with their affairs."

This Hadith was deemed weak by Al-Albani, and Al-Munawi said: "The Hadith is Munkar (denounced)."

Even if we assume the Hadith is authentic, it does not encourage recitation with musical scales (Maqamat). Rather, it encourages improving one's voice and performance without the artificial tunes of singers.

In summary, when reciting, you must pronounce the letters correctly and avoid errors in vocalizations (harakat), while observing the rules of Tajweed, and improving your voice and performance in a way that is reverent and impactful. This is the commanded 'singing' (Taghanni).

As for the artificial recitation with Maqamat, it is not among the permissible manners of recitation; rather, it is blameworthy.

Ibn Al-Qayyim said in Zad Al-Ma'ad: "Melodious recitation (Tatreeb and Taghanni) is of two types: The first type: That which is natural and spontaneous, without affectation, practice, or teaching. This is permissible. The second type: That which is a craft, and cannot be achieved except through affectation, artificiality, and practice. This is what the Salaf (pious predecessors) disliked and condemned."

As for praying behind someone who makes errors in their recitation (yalhan), the prayer is valid but disliked, as long as the error in Al-Fatihah does not alter the meaning. If the meaning is altered, the prayer becomes invalid.

The matter of leading prayer (Imamah) is grave, and it should only be undertaken by the most proficient among the people in reciting the Book of Allah.