She misses Thuhr and ‘Asr prayers because of work
16-9-2015 | IslamWeb
Question:
assalamu ‘alaikum wa rahmatullah wa barakatuh, I am a single mother and I work 9hrs a day in the medical field where I cannot take a break to offer salah. This means I will miss Dhuhr and Asr prayers. Does that mean that when I make them up once I get home that Fajr, Maghrib, and Isha are then invalid, or does that mean that dhuhr and Asr are invalid?
Answer:
All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad 
is His Slave and Messenger.
Delaying a given prayer, even without a valid excuse, does not cause another prayer that was performed in the proper time to be invalid. This prayer is valid and you are sinful for delaying the other ones without a valid excuse and it is obligatory that you make them up.
If you mean that you delay both Thuhr and ʻAsr prayers and perform them when you go home after sunset, you should know that it is impermissible to delay the Thuhr and ʻAsr prayers until after sunset under any circumstances. The reason that you mentioned in the question is not a valid justification to delay the prayers after their proper times. It is inconceivable that you have absolutely no break during the nine hour work day, as performing the prayers does not take long. We advise you to perform the prayers on time for fear of Allaah. We do not see a valid excuse for you to delay the prayers. Please refer to Fataawa 84802 and 86684.
However, if you performed the Thuhr and ʻAsr prayers before sunset, then the matter is less serious. The ʻAsr prayer in this case would have been performed before its time was finished and you would have only missed the Thuhr prayer. However, it is impermissible to delay ʻAsr prayer until the sun turns yellow except in case of a real need as underlined in Fatwa 275422. It is impermissible to delay the Thuhr prayer until the time for ʻAsr prayer unless the person intends to combine the two prayers. In such a case, it would be permissible to delay the Thuhr prayer. Some jurists held that it is permissible for settlers (non-travelers) to combine the Thuhr and ʻAsr prayer in case of a need provided that it does not turn into a habit as highlighted in Fataawa 82828 and 99903 about the settler combining prayers due to a (pressing) need and the conditions for permissibility of that.
Allaah Knows best.