Musannaf Ibn Abi Shaybah

It is narrated from Hazrat Muadh bin Jabal, he says that one day we waited a long time for the arrival of the Prophet (peace and blessings be upon him) for the Isha prayer, but he delayed so much that a man said that he will not come. Meanwhile, the Prophet arrived, so a man said, "O Messenger of Allah! We thought that you had already performed the prayer and would not come now." The Prophet (peace and blessings be upon him) said, "Pray this prayer in the darkness of the night, because you have been given superiority over all other nations due to this prayer; the nations before you did not perform this prayer."

Hazrat Jabir narrates that the Prophet (peace and blessings be upon him) asked Hazrat Abu Bakr, "When do you perform Witr?" He replied, "At the beginning part of the night, after 'Isha, before sleeping."

Hazrat Ibn Abbas (may Allah be pleased with them) says that if you have to travel up to the time of the night (‘Isha) prayer in a day, then do not shorten the prayer; but if you have to travel more than the time of the night (‘Isha) prayer, then shorten the prayer.