Is it considered negligence on my part for the sustenance of my wife when my wife work? The reason is after paying all of my monthly commitments, I’ll only have RM300 and this doesn’t include my wife’s sustenance. Hope for an answer.
Alhamdulillah, praise and gratitude to Allah SWT for His countless blessings for us all. Praise and salutations to our beloved Prophet Muhammad PBUH, his family, companions, and all those who follow his footsteps until the Final day.
Sustenance lexically means providing, which means financially providing for his family. While in syarak, it means a provision in terms of food, clothing, shelter and others. It is named Nafaqah for it is spent for this need. 
In al-Sunnah, there is a hadith narrated from Mu’awiyah al-Qusyairi RA, where he asked the Prophet PBUH: “O Messenger of Allah, what is the rights of a wife on one of us of which is obligated for her husband?” Rasullullah PBUH replied:
أن تُطْعِمَها إذا طَعِمتَ ، وتَكْسوها إذا اكتسَيتَ ، أوِ اكتسَبتَ ، ولا تضربِ الوَجهَ ، ولا تُقَبِّح ، ولا تَهْجُرْ إلَّا في البَيتِ
“That you should give her food when you eat, clothe her when you clothe yourself, do not strike her on the face, do not revile her or separate yourself from her except in the house.” 
Syeikh Wahbah al-Zuhaili said the majority of scholars stated the obligatory sustenance to be given to a wife are the following seven matters which are, food, groceries, clothing, house, personal hygiene appliances, houseware, assistant for his wife is his wife usually has an assistant. 
Scholars have agreed (ijma’) that the husband is obligated to provide sustenance for his wife. Furthermore, this still applies even if his wife works and has her own income and wealth. The responsibility of the family’s sustenance is on the husband. This is based on the statement of Allah SWT:
وَٱلۡوَٰلِدَٰتُ يُرۡضِعۡنَ أَوۡلَٰدَهُنَّ حَوۡلَيۡنِ كَامِلَيۡنِۖ لِمَنۡ أَرَادَ أَن يُتِمَّ ٱلرَّضَاعَةَۚ وَعَلَى ٱلۡمَوۡلُودِ لَهُۥ رِزۡقُهُنَّ وَكِسۡوَتُهُنَّ بِٱلۡمَعۡرُوفِۚ
“Mothers may breastfeed their children two complete years for whoever wishes to complete the nursing [period]. Upon the father are the mothers’ provision and their clothing according to what is acceptable.” 
Ibn Kathir stated in his commentary that it is obligatory for the father to provide in terms of appropriate clothing which is customarily accepted in the country without being wasteful or burdensome. It is in accordance with his (the father) financial capability in times of ease and moderate as well as what he is used to. 
In the issue of sustenance, it should be properly understood. The reason is sustenance is a crucial element in marriage and included under the responsibility of the husband over his wife under his care.
In the discussion of sustenance, jurists have divided it into three groups of husbands, the wealthy, average and low income. If the husband is poor then it is sufficient for him to provide the basic sustenance, such as one mudd of rice as well as basic dishes accompanying the rice according to the local custom. Next, the basic clothing for his wife to wear following the local custom when she is at home or outside, covering her aurah. Then, provide a place to live according to his capability, without it being conditioned that he owns the house, it is enough if he’s only able to rent it. If the poor husband fulfils all these basic needs, then the wife doesn’t have a right to demand a fasakh. 
One should realize that marriage comes with responsibilities for both the husband and wife. However, believe that Allah SWT will never burden or even oppress a husband. Believe that everything that is sanctioned by Allah SWT has great wisdoms behind them. This is as clearly stated by Allah SWT in the Quran:
لِيُنفِقْ ذُو سَعَةٍ مِّن سَعَتِهِ ۖ وَمَن قُدِرَ عَلَيْهِ رِزْقُهُ فَلْيُنفِقْ مِمَّا آتَاهُ اللَّـهُ ۚ لَا يُكَلِّفُ اللَّـهُ نَفْسًا إِلَّا مَا آتَاهَا ۚ سَيَجْعَلُ اللَّـهُ بَعْدَ عُسْرٍ يُسْرًا
“Let a man of wealth spend from his wealth, and he whose provision is restricted – let him spend from what Allah has given him. Allah does not charge a soul except [according to] what He has given it. Allah will bring about, after hardship, ease.” 
According to the above question, it is obligated for a husband to provide sustenance for his wife regardless of whether it is a little or a lot even if his wife is working. The reason is it is the responsibility of a husband to fulfil the needs of his wife and children according to his capability. However, the husband is free from this obligation if his wife is fine and gives her permission for him to not provide for her. Aisyah R.Anha once narrated that one day, Hindun, who is the mother of Muawiyah came to Allah’s Messenger (ﷺ) and said, “O Allah’s Messenger, Abu Sufyan is a miser who does not give me and my sons enough maintenance, except what I take from his wealth without his knowledge. Is there any blame on me for doing this?” He replied,
خُذِي مَا يَكْفِيكِ وَبَنِيكِ بِالْمَعْرُوفِ
“Take from his wealth what is reasonable and enough for you and your sons.” 
This hadith is proof that it is permissible to take from the property of a husband without his knowledge according to the needs of the wife if her husband is stingy and doesn’t provide sustenance for his family.
To close, we advise you to rearrange your financial priorities according to your capabilities and include your wife’s sustenance in your monthly commitments. We also suggest for you employ the services from the Credit Counseling & Management Agency (AKPK) if in need of assistance for financial management.
If the wife is content with her husband not financially providing for her, then the husband is free from this responsibility, however, the matter of concern here is if some other issues arise later, there is a possibility that the wife will raise this issue and it will lead to a greater problem regarding this issue of sustenance. Our advice for the husband is to be determined in managing his family sustenance properly. One should always discuss wisely with one’s wife. We’d also suggest drafting a plan of action together in managing the family’s finances.
May Allah gives us the correct understanding of this religion. We end with the supplication:
اللَّهُمَّ اكْفِنِى بِحَلاَلِكَ عَنْ حَرَامِكَ وَأَغْنِنِى بِفَضْلِكَ عَمَّنْ سِوَاكَ
“O Allah, suffice me with what You have allowed instead of what You have forbidden, and make me independent of all others besides You.”
 See al-Mu’tamad fi al-Fiqh al-Syafie, 4/274
 Narrated by Abu Dawud (2142), Ibn Majah (1850) and Ahmad (20013)
 See al-Fiqh al-Islam wa Adillatuh, 10/7349
 See Tafsir Ibn Kathir, 1/634
 See al-Mu’tamad fi al-Fiqh al-Syafie, 4/283
 Narrated by al-Bukhari (3825), Muslim (1714), Abu Dawud (3532), al-Nasaie (5420), Ibn Majah (2293) and Ahmad (24163)