Is one who intended to combine the Dhuhr and Asr prayers by delaying them during travel, then was overtaken by the Maghrib adhan before he could pray due to an unforeseen emergency, considered sinful, despite his attempt to rectify the situation?

It is prescribed for the traveler to combine the Dhuhr and Asr prayers, and the Maghrib and Isha prayers, either by performing them earlier (jama' taqdim) or delaying them (jama' ta'khir). If you intended to combine Dhuhr with Asr by delaying them before their time expired, there is no harm in that. Delaying the prayer until the time for Maghrib enters, if it was not due to negligence or deliberate intention, then you will not be held accountable for it, based on the Almighty's saying: "And there is no blame upon you for that in which you have erred, but [only for] what your hearts intended," and based on the Prophet's (peace be upon him) saying: "Indeed, Allah, the Almighty and Majestic, has overlooked for my Ummah errors, forgetfulness, and what they are forced to do." The rulings on the traveler's prayer can be found in books of Hadith (definition) and Fiqh. Among the recommended books is "Salat al-Musafir" by Sheikh Saeed Al-Qahtani.