According to the provided reference, Prophet Salah (علیہ السلام) is credited with the discovery of soap.
Here's a summary of inventions attributed to different prophets as mentioned in the reference:
| Invention | Prophet |
|---|---|
| Soap | Prophet Salah (علیہ السلام) |
| Bridge | Prophet Yousuf (علیہ السلام) |
| Boat | Prophet Nooh (علیہ السلام) |
| Mirror | Prophet Sulaiman (علیہ السلام) |
Therefore, based solely on the given information, the answer is Prophet Salah (علیہ السلام).
