This letter, written to Mawlana Muhammad Sadiq Kashmiri, explains the difference between the 'ilm-ul- yaqin of the men of tasawwuf and the 'ilm-ul-yaqin of philosophers:

Hamd be to Allahu ta'ala! Salam to those slaves of His chosen and loved by Him! According to men of tasawwuf, 'ilm-ul-yaqin means to infer the agent of the work by seeing the work, and also philosophers who follow the way of understanding and judging everything under the guidance of the mind. What is the difference between these two? Why does the 'ilm-ul-yaqin of men of tasawwuf get formed through kashf and shuhud? Why is the 'ilm-ul-yaqin of those savants of the din who are not men of tasawwuf like that of philosophers? We shall explain these briefly. In both types of 'ilm-ul-yaqin it is necessary to see the work. A path through the work will lead to the unseen doer. The path that leads man to the doer from the work is the relation between these two. In the 'ilm-ul-yaqin of the men of tasawwuf, this relation is seen through kashf and shuhud, too. But in the 'ilm-ul- yaqin of savants of the din and of philosophers this relation is understood through the mind, by thinking and observing. For this reason, men of tasawwuf's recognizing the doer from the work is hadsi (inductive, intuitive). That is, it happens automatically and spontaneously. In fact, it is badihi, that is, it is obvious, quite clear. But the others' understanding the doer by seeing the work is by thinking, observing. As it is seen, the 'ilm- ul-yaqin of men of tasawwuf is through kashf and shuhud. But the others' ilm-ul-yaqin cannot be formed without observing with the mind. The 'ilm-ul-yaqin of men of tasawwuf also is called istidlal, that is, thinking, yet it is called so because inferring the doer from the work is given this name. In actual fact, it is not istidlal, but it is kashf and shuhud. The 'ilm-ul-yaqin of savants of the din is through istidlal. Many people could not understand this subtle difference. Some of them spoke ill of great men of tasawwuf. Allahu ta'ala, alone, communicates the truth of every matter. May our salam be upon those who are on the right way!