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, sallallaahu ‘alayhi wa sallam, is His slave and messenger.
There is no blame in undertaking activities related to Da‘wah during office hours or in utilizing the computer and electricity as long as:
- The institution where you work pays a fixed sum of money for internet service regardless of the extent of usage.
- The institution gives you permission to use the computer for your activities and agrees to pay for the electricity and other expenses for the time you use it.
- Undertaking these activities does not negatively affect the quality of customer service you provide.
If all these conditions are satisfied, you will not be blamed, rather you will be rewarded by Allaah for your efforts in the field of Da‘wah. It was narrated that the Prophet, sallallaahu ‘alayhi wa sallam, said that If anyone calls others to guidance, his reward will be equivalent to those who follow him without their reward being diminished in any respect. [Muslim]
However, if the institution does not permit such activities, or refuses to pay the extra expenses (if any), then it is impermissible for you to use your working hours for Da‘wah.
After all, you should keep in mind that calling to Allaah The Almighty is one of the noblest goals a Muslim can have and this should not be achieved through prohibited means. This is because ends don’t justify evil means.
If you were using the computer and internet without permission, you could inform your supervisors about this; if they give you permission, it would be good. Otherwise, you are obliged to pay the expenses of using the computer, internet service, and electricity for the above-mentioned activities. If it is impossible to calculate the expenses exactly, then it would be sufficient to approximate these expenses as fairly as possible. Allaah Knows best.