Answer
Wa `alaykum as-Salamu wa Rahmatullahi wa Barakatuh.
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
In this fatwa:
If waist training is taken as a medical treatment, it is allowed. Body modification, which is forbidden, is changing Allah’s original creation.
In his response to your question, Sheikh Ahmad Kutty, a senior lecturer and an Islamic scholar at the Islamic Institute of Toronto, Ontario, Canada, states:
If waist training is prescribed by a medical professional specializing in treatments for such conditions, then it is permissible.
In such a case, waist training is akin to fixing a crooked tooth or making corrective surgeries to repair deformities.
The Prophet (peace be upon him) has allowed resorting to corrective methods of treatments in similar cases.
So, interference with the body is forbidden if it amounts to altering or disfiguring the original creation of Allah.
On the other hand, it is permissible when undertaken to enhance the creation.
Allah Almighty knows best.
Editor’s note: This fatwa is from Ask the Scholar’s archive and was originally published at an earlier date.