Whenever the Messenger of Allah ﷺ was traveling, he would pray two rakats.
حدثنا وكيع عن إسرائيل عن أبي إسحاق عن سعيد بن شفي
كان رسول الله ﷺ إذا كان مسافرا صلى ركعتين
No references are available.
Its isnad is sahih, despite the possible break in it, and we have discussed this in detail at 2159, 2160, 2575, and see also 2334.