Abdullah bin Abbas (may Allah be pleased with him) says: The Messenger of Allah (peace and blessings be upon him) prescribed two rak'ahs of prayer during travel, and this is the complete prayer, and offering Witr during travel is Sunnah.

Sayyiduna Abdullah bin Umar (may Allah be pleased with him) narrates that the Messenger of Allah (peace and blessings be upon him) used to perform only two rak‘ahs of prayer during travel, but he would offer Tahajjud at night. Jabir asked Salim: Did (the Noble Prophet, peace and blessings be upon him, and Sayyiduna Abdullah, may Allah be pleased with him) perform Witr during travel? He replied: Yes.

Hafs bin Asim says: We went out with Sayyiduna Abdullah bin Umar (may Allah be pleased with him) and (at one place) performed the obligatory prayer. Then Sayyiduna Ibn Umar (may Allah be pleased with him) saw that some of his sons were performing the Sunnah prayers, so he said: I have performed prayers with the Noble Prophet (peace and blessings be upon him), Sayyiduna Abu Bakr, Sayyiduna Umar, and Sayyiduna Uthman (peace and blessings be upon them), and they did not perform the Sunnah prayers before or after (the obligatory prayer). Then he said: If I had to perform this voluntary prayer, I would have completed (the obligatory prayer as well).

(Second chain of narration) He says: I was on a journey with Sayyiduna Abdullah bin Umar (may Allah be pleased with him), he performed two rak'ahs each for Zuhr and Asr, then he stood up for his mat and, seeing that people were performing voluntary prayers after that, asked: What are these people doing? I said: They are performing nawafil (voluntary prayers). He said: If I had to perform any voluntary prayer before or after the obligatory prayers, I would have completed the obligatory prayers themselves. I remained in the company of the Noble Prophet (peace and blessings be upon him) until his passing, and he (peace and blessings be upon him) did not perform more than two rak'ahs, then I remained with Sayyiduna Abu Bakr (may Allah be pleased with him) until his passing, he too did not perform more than two rak'ahs, then Sayyiduna Umar and Sayyiduna Uthman (may Allah be pleased with them) also did the same.