Working time must be for work only as long as there is a task that has to be done and there is no spare time. Any employee has made a contract with his employer to do a specific job in a specific time, so it is not allowed for him to use this time any other thing than his work. Allah says in the Qur’an (O you who believe! Fulfil (your) obligations) (Al-Ma’idah 5:1)
The Prophet (peace and blessings be upon him) said also “The Muslims are bound by their conditions.” (Abu Dawud)
In his response to this issue, Sheikh Salim `Abdus-Salam Ash-Shaykhi, a da`iyah said that ‘when a person is at work, his time is for his work and he should devote himself to his work. However, if there is no work to be done and he has time at hand, it is permitted to do the things that he desires provided his employer understands that and permit it. However, if doing that thing is going to affect his work quality or quantity then it is not permitted.