Question Summary:
What is the wisdom behind the left thigh speaking first on the day of judgment?

Question Detail:

 What is the wisdom behind the left thigh speaking first on the day of judgment?

Answer :

In the Name of Allah, the Most Gracious, the Most Merciful.
As-salāmu ‘alaykum wa-rahmatullāhi wa-barakātuh.
The hadith in reference is below:
عن عقبة بن عامر، أنه سمع النبي صلى الله عليه وسلم يقول: إن أول عظم من الإنسان يتكلم يوم يختم على الأفواه، فخذه من الرجل الشمال (مسند أحمد ج-٢٨ ص-٦٠٢، مؤسسة الرسالة)
Narrated by ‘Uqbah bin ‘Āmir, he heard Nabī (salla Allahu ‘alaihi wa sallam) saying: The first limb of a person to speak on the day the mouths will be sealed is his left thigh.
The testification of the limbs on the Day of Judgment is established in verse 65 of Surah Yāsīn:
اليوم نختم على افوههم وتكلمنا أيديهم وتشهد أرجلهم بما كانوا يكسبون (يس:٦٥)
Today we shall seal their mouths and their hands will speak and their legs will testify to their actions     (Yāsīn: 65)
The affairs of the Hereafter and their realities are hidden. As such, explaining the wisdoms of the incidents and occurrences which will take place in the Hereafter are at most conjecture. Though it is permissible to inquire of the wisdom of such things, it is advisable that one inquires regarding things which are more pertinent to his dīn. Furthermore, though one may initially (and innocently) ask of the wisdoms of Allah’s laws, system, etc. he may be lead to questioning and criticizing Allah’s “reason” eventually.
And Allah Ta’āla Knows Best
Hisham Dawood
Student, Darul Iftaa
Chicago, USA
Checked and Approved by,
Mufti Ebrahim Desai.
www.daruliftaa.net