All perfect praise be to Allah, the Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
There is no doubt that the scholars have a great status in Islam. Islam considers the scholars as the inheritors of the prophets since they carry the religion to the laypeople. Allah Almighty assigns the Muslim scholars as witnesses to the truth and associates their testimony with that of Allah and that of His Angels. Allah Almighty says: {Allah witnesses that there is no deity except Him, and [so do] the angels and those of knowledge – [that He is] maintaining [creation] in justice. There is no deity except Him, the Exalted in Might, the Wise.} [Quran 3: 18]
If criticizing scholars is intended to slander them and find faults with them, then such criticism is not allowed because the Muslim is forbidden to harm his fellow Muslim, let alone scholars who must be given due respect. Ibn ‘Umar and his father, narrated that the Prophet, sallallaahu ‘alayhi wa sallam, said:
O those who believed by tongue and the belief has yet to enter their hearts! Do not back-bite Muslims, and do not pursue their faults and failures. If someone pursues someone else’s faults, Allah will expose his faults, and if Allah exposes someone’s faults, He will disgrace him even if he is inside his home. [Ahmad, Abu Dawood, An-Nasa’i, Ibn Majah, and At-Tirmithi]
Ibn ‘Asakir says, “The honor of the scholars is sacred and it is the norm of Allah to take revenge on those who slander them. Whoever gives full reign to his tongue to insult the scholars and expose their faults, Allah will cause his heart to die within his body.”
However, if you criticize a scholar in order to clarify something that he has made a mistake about and you do this in a respectful manner, then this is acceptable, or even recommended, in some cases. The Muslim is required to share whatever he knows about Islam with others. If the Muslim hears a Muslim scholar make a mistake, then he should clarify this mistake in a respectful and wise manner and, more importantly, substantiate his clarification with textual evidence from Islamic tradition.
Our righteous predecessors used to write responses to one another; however, they would be committed to ethical standards in their writings. Similarly, part of Hadith criticism (a discipline of Islamic knowledge) is concerned with scrutinizing prophetic statements and verifying the reliability of Hadith narrators.
Allah knows best.