Shaykh Sālih al-Fawzān [حفظه الله] said:
❝The individuals who ascribe themselves to [giving] Da’wah, it is mandatory that they be investigated:
• Where did they study?
• Where did they take knowledge from?
• Where were they reared?
• What are their beliefs?
• Their actions must be investigated, their effects upon the people, along with what good they have brought about.
• What rectification has their actions produced?
Their affairs must be investigated before [the people] are misled by their statements and what is apparent from them. This investigation is mandatory, especially during the present time in which the callers of Fitnah are many.❞
[Al-Ijaabaatul-Muhimmatu Feel-Mashaakilil-Mulimmah, (Page: 34) | Translated By Abū Ismāīl Muṣṭafā George]