The Sunnah for him is to pray each prayer on time and not to join except in need or for a necessity. Joining while he is in his apartment and without any need is not in accordance to the Sunnah.

And Allah knows best

My husband has gone to another country for a few months on work,he is praying the travelling prayers and joining zuhar and asr and then maghrib and isha together. My question is if that is permissable to do when he can easily pray the qasr prayers on each prayer time.for example he is in his apartment by maghrib so he can pray 3 fard of maghrib ,then when Isha time comes he can pray the two fard of Isha,instead of praying them together.Can he do this also?