Shaykhul Islaam Ahmad ibn Taymeeyah 728AH (May Allah have mercy on him) said,

العالم يعرف الجاهل لأنّه كان جاهلا، والجاهل لا يعرف العالم لأنّه ما كان عالما

“The scholar recognizes the one who is ignorant because he was once ignorant. However, the ignorant does not recognize a scholar because he was never one of them.”

Source: Jawaab al-‘itiraadaat al-Masriyah 172