Your answer is given by the household of the holy prophet --peace be upon him and his household, the describers of Quran, as follows:
محمد بن يعقوب: عن علي بن إبراهيم، عن أبيه، و علي بن محمد، عن القاسم
بن محمد، عن سليمان بن داود المنقري، عن علي بن هاشم بن البريد، عن أبيه:
أن رجلا سأل علي بن الحسين (عليهما السلام) عن الزهد فقال: «عشرة أشياء
فأعلى درجة الزهد أدنى درجة الورع، و أعلى درجة الورع أدنى درجة اليقين،
و أعلى درجة اليقين أدنى درجة الرضا، [ألا] و إن الزهد كله في آية من
كتاب الله عز و جل: لِكَيْلا تَأْسَوْا عَلى ما فاتَكُمْ وَ لا
تَفْرَحُوا بِما آتاكُمْ».
A man asked from Imam Sajjad --peace be upon him-- about Zuhd
(asceticism). Imam answered: "... the uppest degree of asceticism is
the closest (lowest) level of pious, and the highest level of pious is
the lowest level of certainty, and the highest level of certainty is
the lowest degree of satisfaction. Know that the whole of Zuhd is
considered in one verse of the book of Allah: In order that ye may
not despair over matters that pass you by, nor exult over favours
bestowed upon you. For Allah loveth not any vainglorious boaster"
علي بن إبراهيم، قال: حدثني أبي، عن القاسم بن محمد، عن سليمان بن داود
المنقري، عن حفص بن غياث، عن أبي عبد الله (عليه السلام)، قال: قلت: جعلت
فداك، فما حد الزهد في الدنيا؟ قال: فقال: «قد حد الله في كتابه، فقال عز
و جل: لِكَيْلا تَأْسَوْا عَلى ما فاتَكُمْ وَ لا تَفْرَحُوا بِما
آتاكُمْ إن أعلم الناس بالله أخوفهم لله، و أخوفهم له أعلمهم به، و
أعلمهم به أزهدهم فيها».
Imam Sadiq --peace be upon him-- was asked about the limit of Zuhd in
this life. Imam answered that Allah has determined its limit in His
book, so He has stated "In order that ye may not despair over
matters that pass you by, nor exult over favours bestowed upon you.
For Allah loveth not any vainglorious boaster". The most
knowledgeable people about Allah are the most fearful of Allah, the
most fearful people of Allah are the most knowledgeable of them about
Dunya(?), and the most knowledgeable of them about Dunya are the most
ascetic of them in Dunya.
Source: البرهان في تفسير القرآن، ج5، ص: 298
Therefore Quran defines the Zuhd (asceticism) in this verse:
لِّكَيْلَا تَأْسَوْا عَلَىٰ مَا فَاتَكُمْ وَلَا تَفْرَحُوا بِمَا
آتَاكُمْ ۗ وَاللَّـهُ لَا يُحِبُّ كُلَّ مُخْتَالٍ فَخُورٍ
In order that ye may not despair over matters that pass you by, nor
exult over favours bestowed upon you. For Allah loveth not any
vainglorious boaster [57:23]
But let me explain this to some extent. An ascetic person in Islam may be rich or poor in property; Zuhd does not require the person to have less or least wealth (as was considered by many famous Sufi's in the history of Sufism), but it does require the person not to rely on his wealth, income, and etc., be it a house or car or money in bank or credit or even children or honor, or even healthy body and sharp mind or knowledge or any other possession or characteristic. The ascetic person would always remind his position in the course of life and in the relation with God, so that he only relies on Allah, neither he will get disappointed when he lose something that he had and nor will he exult when he gains something that he had not. In every instant he knows that he is a servant of Allah, he still has some duties even though the conditions of the game will change slightly.
Then we turn back to see the history, we have Talut and Dhul-Qarnein and the prophets Joseph and David and Solomon --peace be upon them-- which were king (or anyway ranked among the highest in a government) with lots of wealth. They were all ascetic of course while were rich as well. Another example if the prophet Ayyub --peace be upon him-- who was rich as well, then Allah examined him by taking back from him almost anything that was given to him, but he remained a good servant of Allah with no single instant of thinking bad (سوء الظن) about his Lord:
وَأَيُّوبَ إِذْ نَادَىٰ رَبَّهُ أَنِّي مَسَّنِيَ الضُّرُّ وَأَنتَ
أَرْحَمُ الرَّاحِمِينَ / فَاسْتَجَبْنَا لَهُ فَكَشَفْنَا مَا بِهِ مِن
ضُرٍّ ۖ وَآتَيْنَاهُ أَهْلَهُ وَمِثْلَهُم مَّعَهُمْ رَحْمَةً مِّنْ
عِندِنَا وَذِكْرَىٰ لِلْعَابِدِينَ
And (remember) Job, when He cried to his Lord, "Truly distress has
seized me, but Thou art the Most Merciful of those that are merciful."
/ So We listened to him: We removed the distress that was on him, and
We restored his people to him, and doubled their number,- as a Grace
from Ourselves, and a thing for commemoration, for all who serve Us.
وَاذْكُرْ عَبْدَنَا أَيُّوبَ إِذْ نَادَىٰ رَبَّهُ أَنِّي مَسَّنِيَ
الشَّيْطَانُ بِنُصْبٍ وَعَذَابٍ / ارْكُضْ بِرِجْلِكَ ۖ هَـٰذَا
مُغْتَسَلٌ بَارِدٌ وَشَرَابٌ / وَوَهَبْنَا لَهُ أَهْلَهُ وَمِثْلَهُم
مَّعَهُمْ رَحْمَةً مِّنَّا وَذِكْرَىٰ لِأُولِي الْأَلْبَابِ / وَخُذْ
بِيَدِكَ ضِغْثًا فَاضْرِب بِّهِ وَلَا تَحْنَثْ ۗ إِنَّا وَجَدْنَاهُ
صَابِرًا ۚ نِّعْمَ الْعَبْدُ ۖ إِنَّهُ أَوَّابٌ
Commemorate Our Servant Job. Behold he cried to his Lord: "The Evil
One has afflicted me with distress and suffering!" / (The command was
given:) "Strike with thy foot: here is (water) wherein to wash, cool
and refreshing, and (water) to drink." / And We gave him (back) his
people, and doubled their number,- as a Grace from Ourselves, and a
thing for commemoration, for all who have Understanding. / "And take
in thy hand a little grass, and strike therewith: and break not (thy
oath)." Truly We found him full of patience and constancy. How
excellent in Our service! ever did he turn (to Us)! [38:41-44]
That's a very common examination style that Allah puts forward in our courses of lives, to give us for us to remind Him and thank Him (both by doing our duties and by tongue) or to take back from us again to remind Him and ask Him and be patient, being pleased by what Allah has chosen for us.
This is only a short argument about Zuhd, you can easily extend your knowledge by many great books written based on this verse and the Ahadeeth of the 14 infallibles peace be upon them.