There is a Hadith in Khasaais-e-Kubra on the authority of Hadhrat ‘Abdullah bin ‘Abbas (May Allah be well pleased with them) that some people from Hadhramaut came to the Holy Prophet (Sallallahu alaihi wa sallam). Ash’ath bin Qais was also among them.
They said: We are concealing something in our hearts from you. You tell us what it is. The Holy Prophet (Sallallahu alaihi wa sallam) replied: Sublime is Allah! That is the work of a sorcerer and the place for a sorcerer and sorcery is hell.
They said: How can we know then that you are the Prophet of Allah?
The Holy Prophet (Sallallahu alaihi wa sallam) picked up a fistful of sand and said: See! They are testifying that I am the Prophet of Allah. Thus, those pebbles recited the testification of faith in the blessed hands of the Holy Prophet (Sallallahu alaihi wa sallam).
On listening to this, they also declared: We testify that indeed you are the Prophet of Allah (Sallallahu alaihi wa sallam).
There are various other Hadith like this which show that pebbles recited the testification of faith in the blessed hands of the Holy Prophet (Sallallahu alaihi wa sallam).
There is no doubt that the Holy Prophet (Sallallahu alaihi wa sallam) was aware of what the hearts concealed, the proof of which are many Hadith in this regard. However, on this occasion, the Holy Prophet (Sallallahu alaihi wa sallam) said that this is the work of sorcerers. It might be that if the Holy Prophet (Sallallahu alaihi wa sallam) had revealed what they were hiding, they would have gotten the chance to say that even sorcerers did that and it was also possible that that thought would have assailed them with doubt. For this reason, the Holy Prophet (Sallallahu alaihi wa sallam) expressed a miracle which was impossible for anyone else.
It is written in Seeratun Nabawwiyya at the conclusion of this Hadith that the Holy Prophet (Sallallahu alaihi wa sallam) asked them: Have you not embraced Islam? They said: Yes, why not! The Holy Prophet (Sallallahu alaihi wa sallam) said: Then how can you wear silk clothes? On hearing this, all of them tore away their silk clothing.
Praise be to Allah! This is Islam. The moment they learned that silk is prohibited, the tore away those garments. Unlike us who know everything but don’t act on it. May Allah grant us true faith which will make acting on its commands easy for us.