Is it permissible to shorten and combine prayers at the workplace in Cairo, knowing that the questioner has been working there for 15 years and resides in Faiyum, which is 100 km away from Cairo?

It is permissible to shorten and combine prayers for a traveler between his home and work if the prayer time overtakes him at work or on the way, and there is no need to repeat them. However, if a congregational prayer is established at the workplace or in one of the town's mosques, then one must pray with them fully. The evidence for the permissibility of shortening prayers comes from the general prophetic traditions, including the Hadith of Anas: "I prayed with the Messenger of Allah, peace and blessings be upon him, Dhuhr in Medina four rak'ahs, and I prayed with him Asr at Dhu al-Hulayfah two rak'ahs."