Is it permissible to stitch shrouds?

The Sunnah is to shroud the deceased in three pieces of cloth which are to be wrapped around him, as was done to the Messenger of Allah (blessings and peace of Allah be upon him). It was narrated from `A’ishah (may Allah be pleased with her) that the Messenger of Allah (blessings and peace of Allah be upon him) was shrouded in three pieces of white cotton cloth from Yemen, among which there was no chemise or turban. Narrated by al-Bukhari, 1264, and Muslim, 941.

If he is shrouded in something other than that, such as in a chemise and the like, there is nothing wrong with that, but following the Sunnah is better.

The minimum in which the deceased person may be shrouded, which fulfils what is required, is a single piece of cloth that covers the entire body.

See the answers to questions no. 98308 and 98409.

A woman is to be shrouded in five pieces of cloth: a waist wrapper, a chemise, a headcover and two wrappers.

Please see also the answer to question no. 98189.

Based on that:

What is required with regard to shrouding the deceased is to cover the entire body, so if it is covered with any kind of cloth, that requirement has been met, and nothing specific has been stipulated regarding that. So if a person is shrouded in the clothes which he was wearing, or a specific garment is sewn for him, there is nothing wrong with that, but paying attention to the Sunnah and wrapping him in a piece of cloth that is not not tailored to the shape of the body like the clothes of the living, is better.

The scholars of the Permanent Committee said:

What is required is to shroud the deceased in something that will cover him, and the Sunnah is to shroud a man in three pieces of white cloth, wrapping it around him. But if he is shrouded in his regular clothing, such as a jacket, pants and a shirt, or clothes are sewn for him with sleeves and the like, like the clothes he wore in this world, that is sufficient, but it is contrary to the Sunnah which was the practice at the time of the Prophet (blessings and peace of Allah be upon him) and his companions.

End quote from Fatawa al-Lajnah ad-Da’imah, 8/430.

But if the cloth of the shroud is short, or it is too narrow, so another piece is stitched to it so that it will cover the entire body when he is wrapped in it, there is nothing wrong with that, and that does not go against the Sunnah mentioned above.

And Allah knows best.