Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) would not perform any voluntary (nafl) prayers along with the obligatory (fard) prayers during travel—neither before the obligatory prayers nor after them—except at night after dismounting on the ground, and sometimes he would perform voluntary prayers on his camel, even if the camel was not facing the qiblah.

Imam Malik, may Allah have mercy on him, was informed that Hazrat Qasim bin Muhammad, Hazrat Urwah bin Zubair, and Hazrat Abu Bakr bin Abdur Rahman used to offer Nafl prayers while traveling.
Imam Malik, may Allah have mercy on him, was asked about offering Nafl prayers during travel. He replied that there is nothing wrong with it, whether at night or during the day, and I have received from some people of knowledge that they used to offer Nafl prayers while traveling.

It is narrated from Hazrat Nafi that Sayyiduna Abdullah bin Umar (may Allah be pleased with them) used to see his son Ubaidullah performing voluntary prayers during travel, and he would not object to him for this.

It is narrated from Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) that I saw the Messenger of Allah (peace and blessings be upon him) praying on a donkey, and his face was towards Khaybar.

It is narrated from Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) used to pray on a camel during travel, facing in the direction the camel was facing. Abdullah bin Dinar said that Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) also used to do the same.

It is narrated from Yahya bin Saeed that I saw Sayyiduna Anas (may Allah be pleased with him) performing prayer while traveling on a donkey, and his face was not towards the Qiblah. He would perform bowing (ruku) and prostration (sajdah) by indication, without placing his face on anything.