The Prophet ﷺ said, "When one of you rises at night, let him begin his prayer with two light rakahs."
حدثنا معاوية قال حدثنا زائدة حدثنا هشام بن حسان عن محمد
عن النبي ﷺ قال إذا قام أحدكم من الليل فليفتتح صلاته بركعتين خفيفتين
Its isnad is sahih. Muslim narrated it in the Prayer chapter, the section on supplication during the night prayer and standing in it, 1/532 no. 768, and Ibn Khuzayma, 1/183 no. 1150.