When the Messenger of Allah ﷺ rose at night to pray, he would begin his prayer with two short rakahs.
حدثنا هشيم عن أبي حرة عن الحسن عن سعد بن هشام
كان رسول الله ﷺ إذا قام من الليل يصلي افتتح صلاته بركعتين خفيفتين
Its isnad is sahih. Abu Hurrah is Wasil bin Abdul-Rahman, who is deemed reliable, though it has been said that he practices tadlis in narrating from Hasan, but this is how it appears in Muslim with its wording and chain. Saad bin Hisham is the Ansari, one of the trustworthy Followers, and his hadith appears in the collections of all the major compilers.The hadith was narrated by Muslim, 1/532, no. 769, in the book of the prayer of travelers, and by Bayhaqi, 3/605.