Is it permissible to delay praying maghrib until isha due to him being tired, for an individual who returned from travelling directly after Maghrib prayer i.e. the time of Maghrib has not exited (but the prayer has been established in the masaajid in congregation)?
Yes, that is permissible, because not combining in this situation would cause difficulty for him. For indeed ‘Abdullah ibn ‘Abbas (May Allah be pleased with them both) said,
‘The Prophet (sallallahu alaihi wa salam) combined between Dhuhr and ‘Asr , and Maghrib and ‘Isha whilst he was in Madeenah, and there was no fear and no rain. They said to him (‘Abdullah ibn ‘Abbas), why is that? He said, He did not want hardship for his ummah’
Shaykh ‘Uthaymeen: meaning that he did not want the ummah to be afflicted with difficulties by not combining (when there is a need).
Fataawa ‘ala At-Tareeq fee Masaa’il Mutanawiyya Pg 296