Is it mustahabb to wash the hands with soap?

Firstly: 

Islamic sharee‘ah is a flexible way that is based on general
principles and holistic foundations governing human conduct. At the same
time it allows room for new developments that occur with changes in time and
place. For example, it does not put undue restrictions on people with regard
to customs and purely worldly actions; rather it gives them the freedom to
act in accordance with what is appropriate to their desires and interests,
and what will benefit them, so long as any given custom is not contrary to
the text of the Qur’an or Sunnah. This is the meaning of what was affirmed
by the fuqaha’ and scholars of usool when they said: The basic principle
with regard to customs is that they are permissible and are allowed. 

Based on that, there is nothing wrong with the Muslim
benefiting from what has been invented or discovered in modern times, such
as cars, airplanes and electricity… and modern means of cleaning the body or
clothes. 

The Muslim is not required to go back to riding camels or
using the kind of cleaning agents that were used by the Prophet (blessings
and peace of Allah be upon him), because these are not worship in which he
is required to follow the Prophet (blessings and peace of Allah be upon
him); rather these are customs and traditions. 

Ash-Shaatibi (may Allah have mercy on him) said: 

With regard to customs, the Lawgiver focused on the idea of
achieving a given purpose, not on a literal following of a shar‘i text,
unlike acts of worship which must be based on a shar‘i text.

End quote from al-Muwaafaqaat, 2/523 

The Prophet (blessings and peace of Allah be upon him)
encouraged cleanliness and that which will protect good health in general
terms, and for that purpose he used the means and things that were available
at his time (blessings and peace of Allah be upon him). If something new is
introduced and it leads to the same purpose (i.e., cleanliness and
maintenance of good health) without causing any harm, then there is nothing
wrong with the Muslim using it and benefiting from it. 

In Islam there are many teachings that are indicative of
paying attention to cleanliness of the body, clothing and place where one
is. To confirm that, it is sufficient to note that wudoo’ – which involves
washing the hands, mouth, nose, and face – is one of the conditions of
prayer, which is the foundation of the faith, being valid. 

Using cleaning agents with water was not widely practised at
the time of the Prophet (blessings and peace of Allah be upon him) because
of the scarcity of these cleaning agents and the scarcity of water itself. 

Yet despite that it is proven in the Sunnah that lotus leaves
may be used in some cases where ghusl is done that require extra attention
to care and cleaning, such as washing the deceased prior to burial, ghusl
for a woman whose period has ended, and ghusl for the kaafir who becomes
Muslim. The fuqaha’ also mentioned using saltwort as well for the purpose of
cleaning and bathing. 

Saltwort (salsola) is a plant that grows in sandy
ground; it or its ash is used for washing clothes and hands.

Al-Mu‘jam al-Waseet, 1/91 

With regard to lotus, this is a plant that grows on water.
Its fruit is the lotus fruit (nabq) and its leaves are used for
washing. See: Lisaan al-‘Arab, 4/354 

It was narrated that Umm ‘Atiyyah al-Ansaariyyah (may Allah
be pleased with her) said: The Messenger of Allah (blessings and peace of
Allah be upon him) entered upon us when his daughter died and said: “Wash
her three times, or five, or more than that, if you see fit, with water and
lotus leaves, and put camphor in the last time, or a little camphor”.

Narrated by al-Bukhaari, 1253; Muslim, 939 

An-Nawawi (may Allah have mercy on him) said: 

This indicates that it is mustahabb or encouraged to use
lotus leaves when washing the deceased. There is unanimous agreement that it
is mustahabb.

End quote from Sharh Muslim, 7/3 

Ibn Rajab (may Allah have mercy on him) said: 

Al-Maymooni said: I read to Ibn Hanbal: Is it acceptable for
the woman whose menses has ended to do ghusl using only water? 

He dictated to me: If she cannot find anything but water on
its own, then she should do ghusl with it. The Prophet (blessings and peace
of Allah be upon him) said: “Your water and your lotus leaves,” and this is
more than ghusl in the case of janaabah. 

I said: What if she did ghusl using water only, then she
found (lotus leaves)? 

He said: I prefer that she should repeat it, because of what
he said.

End quote from Fath al-Baari, 1/471-472 

It was narrated from Qaasim ibn ‘Aasim (may Allah be pleased
with him) that he became Muslim, and the Prophet (blessings and peace of
Allah be upon him) instructed him to do ghusl using water and lotus leaves.

Narrated by at-Tirmidhi, 605. He said: It is hasan. It was
classed as saheeh by al-Albaani in Saheeh at-Tirmidhi. 

It is obvious that using lotus leaves when doing ghusl does
not come under the heading of acts of worship; rather it is the matter of
customs that change with time and place. Whoever uses any cleansing material
in the place of lotus leaves has fulfilled the spirit of the Sunnah and has
fulfilled the purpose for which the Messenger (blessings and peace of Allah
be upon him) instructed people to do ghusl with lotus leaves. 

On our website, in a number of answers, we have explained
that it is not mustahabb to imitate the actions of the Prophet (blessings
and peace of Allah be upon him) that he did on the grounds that they were
customs or personal habits or preferences, and doing so does not bring any
greater reward than other customary matters. Rather reward is attained by
adhering to Sunnahs of worship and related matters. 

Shaykh Dr. Muhammad al-Ashqar (may Allah have mercy on him)
said: 

The ruling on these matters of custom and similar issues is
that they are indicative of something being permissible, and no more, except
in two cases: 

1.    
Where there is a report of
words enjoining or encouraging something, in which case it seems that it is
something prescribed in Islam

2.    
Where it seems that it is
connected to Islam by circumstantial evidence other than words, such as
placing the deceased in his grave facing towards the qiblah. That is
obviously connected to something that is prescribed in Islam.

End quote from Af‘aal ar-Rasool, 1/237 

See also the answer to question no.
69822 

Secondly: 

With regard to what you mentioned about not owning a lot of
clothes, what is required of the Muslim with regard to food, drink and
clothing, and the house in which he lives and the furniture on which he
sits, and other such matters, is that he should not go beyond what he needs.
So what he has of clothing and furnishings should be in accordance with what
he needs and no more than that. If it is more than what he needs, then he
comes under the heading of extravagance which is condemned in Islam. Allah,
may He be exalted, says (interpretation of the meaning):

“and eat and drink but waste not by extravagance,
certainly He (Allah) likes not Al-Musrifoon (those who waste by
extravagance)”

[al-An‘aam 6:141]. 

As-Sa‘di (may Allah have mercy on him) said: 

Extravagance may mean having more than is sufficient and
consuming too much of food that is harmful to the body; or it may mean going
to excess in luxury in food, drink and clothing; or it may mean overlooking
what is halaal and favouring what is haraam. 

“certainly He (Allah) likes not Al-Musrifoon (those who
waste by extravagance)” means that Allah hates extravagance and it is
harmful to the individual’s body and livelihood, because he may end up being
unable to meet his financial obligations. This verse commands us to consume
food and drink and it forbids us to neglect them or be extravagant with
them. End quote. 

Tafseer as-Sa‘di, p. 311 

Ibn Maajah (3605) narrated that the Prophet (blessings and
peace of Allah be upon him) said: “Eat and drink, give charity and wear
clothes, so long as that does not involve any extravagance or vanity.”

Classed as hasan by al-Albaani in Saheeh Ibn Maajah. 

And Allah knows best.