The reality is that stitching is not what is prohibited but that a piece of cloth should not be stitched closed. The Prophet said that when a person is in iḥrām “He should not wear a shirt, nor a turban, nor pants, nor a cloak. He should not wear cloth that has been dyed with wors or saffron…” [Sahīh al-Bukhārī (134) and Sahīh Muslim (1177)] Scholars have derived from this ḥadīth that articles of clothing which are sewn together in order to wrap around parts of the body are prohibited, like pants and shirts. This is because a one piece ‘unstitched’ garment is humble and simple. Stitching up a tear in this garment, for example, is not prohibited. Neither is stitching a pocket into it. Shaykh Ibn Taymiyyah writes: ““If a pair of pants is cut open, it becomes the equivalent of a waistcloth. There is scholarly consensus that it can be wrapped around the waist and worn even when proper waistcloths are unavailable.” [Sharḥ al-ʿUmdah] Shaykh Ibn Taymiyyah: “That which is sewn or bound together for purposes other than to go around a limb – and are not sewn in the shape and size of a limb – can be worn. For instance, a pilgrim can wear a waistcloth or shoulder cloth that is sewn up or that has patches sewn into it. This is because the ruling only prohibits articles of clothing that are designed to fit the limbs of the body. The prohibited articles of clothing are those that are sewn into sleeves and other limb-covering features – the normal clothing that we wear.”
Allah knows best,
Imam Mustafa Umar