[emexiagog]

At the time of the Prophet (saw) soap as we know today didn't exist. In any case when the Prophet (saw) went to a far off place for the toilet he cleaned his hands by wiping on the ground and washing with water. As the earth and water are (natural) purifiers would it be necessary from a fiqh point of view to use soap today? To clarify to remove impurity from the private parts during ghusl water is sufficient, shower gel is just nice to use too!

[LasTins]

I don't know the history of soap use in Arabia during our beloved Prophet's time however, soap is not something new nor are the ingredients difficult to obtain... I wouldn't be surprised if soap was in use in Arabia at the time.

[mrllxp]

Not sure how sound these sources are but thought to share regardless:

The writings attributed to the 8th-century Arab savant Jabir ibn Hayyan (Geber) repeatedly mention soap as a cleansing agent. The Arabs made the soap from vegetable oil as olive oil or some aromatic oils such as thyme oil. Sodium Lye (Al-Soda Al-Kawia) NaOH was used for the first time and the formula hasn't changed from the current soap sold in the market. From the beginning of the 7th century soap was produced in Nablus (Palestine), Kufa (Iraq) and Basra (Iraq). Arabian Soap was perfumed and colored, some of the soaps were liquid and others were hard. They also had special soap for shaving. It was commercially sold for 3 Dirhams (0.3 Dinars) a piece in 981 AD. (source)

and

Islamic history

A 12th century Islamic document has the world's first extant description of the process of soap production.[11] It mentions the key ingredient, alkali, which later becomes crucial to modern chemistry, derived from al-qaly or "ashes".

By the thirteenth century the manufacture of soap in the Islamic world had become virtually industrialized, with sources in Fes, Damascus, and Aleppo. (source)

[imawlBoli]

Perhaps from a Fiqhi point if one can remove the najaasah after going to washroom etc, then that may suffice, however cleanliness in our age and time demands one to use soap, body wash etc,.

We have had a lot of diseases being more prevalent in our time than the time of the Salaf as-Salih. One such example can be HIV/AIDS.