Is it permissible to combine prayers (Dhuhr with Asr and Maghrib with Isha) either by advancing or delaying them due to being absolutely busy, or only in the most dire circumstances, following the example of the Prophet (peace be upon him) and Ibn Abbas (may Allah be pleased with them)?

Ibn Abbas held the view that the Prophet, peace and blessings be upon him, combined two prayers to alleviate hardship for his Ummah. Some imams permitted combining prayers for extreme necessity, such as illness. However, permanent combining of prayers without a reason was considered by some early Muslims (Salaf) to be among the major sins. Scholars differed in interpreting the hadith of Ibn Abbas: the majority held that it was a "pictorial" combining (delaying the first prayer until the end of its time and performing the second at the beginning of its time), while some permitted true combining for the sick or in the case of rain. The fundamental principle is to perform each prayer at its appointed time, and combining is not permissible except out of pressing necessity, not as a routine.