Verification of Speaker and preacher..Person should know from whom he is taking knowledge from..Source of Knowledge
The Usūl of Verification
Many people in this day and age have a problem with the Salafīyyūn in the issue of verification of speakers, this is due to the sole fact that they are extremely lax in checking and verifying the ones whom they take their Dīn/Religion from. They proclaim that there is no need to establish whether one is suitable to take knowledge from or whether one is even from Ahl al-Sunnah. However we know that the Salaf said otherwise.
The great Imām Muḥammad Ibn Sīrīn (d. 110 AH) —
“Indeed this Knowledge is a Matter of Dīn, so be careful whom you take your dīn from.” [The Introduction of Imām Muslim to his Ṣaḥīḥ]
My teacher, Ustāḍ Abū Ḥibbān حفظه الله once mentioned to us in a lecture in respect to the Ṣahābah (رضوان الله عليهم أجمعين)
That the Usūl of verification came from the Nabī ((صلى الله عليه وسلم directly
The proof of that is found in the Ḥadīth Jibrīl in which the Noble Angel Jibrīl (عليه السلام) came in the form of a man to teach the Ṣahābah about their Dīn/Religion.
The Famous Hadīth in which ʿAbd Allāh ibn ʿUmar (رضي الله عنهما) said that his father ʿUmar ibn al Khaṭāb (رضي الله عنه) mentioned to him that "a man appeared before us whose clothes were exceedingly white and whose hair was exceedingly black, We could see no signs of travel on him, but none of us knew him."
Then this "man" (Jibrīl عليه السلام) asked the Nabī (صلى الله عليه وسلم) to inform him about 4 things:
Islām, Īmān, Iḥsān, in which the Noble Angel Jibrīl said, "You have spoken the truth." and then then Jibrīl asked about the Signs of the Hour and after the Nabī (صلى الله عليه وسلم) answered, ʿUmar (رضي الله عنه) said,
"Thereupon the man went off. I waited a while, and then he (the Nabī صلى الله عليه وسلم) said, "O ʿUmar, do you know who that questioner was?"
I replied, "Allāh and His Messenger know better." —
Then, He (the Nabī صلى الله عليه وسلم) said, "That was Jibrīl. He came to teach you your religion."
Therefore our Prophet (صلى الله عليه وسلم) made a point of informing the Sahābah who it was that they were taking their Dīn from.
Written by the one in need of pardon and mercy before his Lord - Abū Ismā’īl Ibrāhīm