What is the criterion for the minor, excusable amount of impurity (al-qadha al-yasir) in ablution according to Ibn Taymiyyah?

Allah does not wish to burden you, and you should cast away these whispers (waswas).

If the speck (qadha) is inside the eye, you do not need to remove it for purification, based on the statement of Imam Al-Shafi'i: "The obligatory part of the face to wash in ablution is what is apparent, not what is hidden, and a man is not required to wash his eyes or sprinkle water into them." In fact, washing the inside of the eye is disliked, even if no harm is feared.

As for what is outside the eye, such as traces of sleep or temporary secretions, it refers back to the fatwa of Ibn Taymiyyah regarding the excused minor barrier. If the secretions are due to an illness that worsens by their removal, then their removal is not obligatory.