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. We ask Allaah to exalt his mention as well as that of his family and all his companions.
It is not permissible to combine the Maghrib and the 'Ishaa’ prayers at the time of Maghrib so that one goes to sleep in order to rest and go to work early, as we clarified in Fatwa 88062.
A Muslim should arrange his time and perform each prayer at its prescribed fixed time. Nonetheless, it is permissible for a Muslim to perform the Maghrib prayer and sleep then wake up before the beginning of the time of Fajr in order to perform the 'Ishaa’ prayer, according to the most preponderant opinion of the scholars . This would be performing it on time and not making it up. An-Nawawi said: 'The time of the permissibility of performing the 'Ishaa’ prayer extends until just before the beginning of the true Fajr; this is the view of our School [Shaafi'ee], and Ash-Shaafi'ee stated this. Also, this is the authoritative opinion of the former and later scholars of our School.'
Therefore, your husband going to sleep sometimes before the 'Ishaa’ prayer and then waking up in order to perform it ['Ishaa’] before the Fajr prayer is something permissible.
It is not disliked to sleep before 'Ishaa’ if one has a sound reason, but if he waits until he performs the 'Ishaa’ prayer and then sleeps, then this is better. Indeed, he may sleep during the day when he comes back from work to make up for the lack of sleep.
Allaah Knows best.