Shama-il Tirmidhi

Amr bin Hurayth radiallahu anhu reports, "I saw rasulullah Sayyidina Rasulullah sallallahu alaihe wasallam perform salaah with such shoes that had another leather sole sewn onto them."

Commentary.
It means that the sole was double. It had two layers of leather. It may also mean that because the shoe was tearing a patch was sewn onto it.