The Wisdom in Timing the Sunnahs of Fitrah at Forty Days

Question:
What is the wisdom in timing the shaving of the head or plucking of the armpits at forty days?

Answer:
Allah knows best. I do not know anything about this, but it may be said, and Allah knows best, that a person may be occupied, or circumstances may arise that prevent him from removing the hair of his private parts, shaving his head, and trimming his beard in less than forty days. Occupations may intervene between him and these acts. So, out of Allah’s mercy, He gave him a wide margin of forty days. This is a form of concession, because he may be occupied, or matters beyond his control may stand in his way. So, out of Allah’s mercy, He gave him a wide margin and covered for him. If it exceeds forty days, peace be upon you. If it exceeds what is apparent in the hadith, the apparent meaning of the hadith which says he should stay [in the state of ihram] for us, and the Prophet (peace and blessings be upon him) [did so], its apparent meaning is pure.