When the Messenger of Allah ﷺ rose at night to pray, he would begin his prayer with two light units.
كان رسول الله ﷺ إذا قام من الليل ليصلي افتتح صلاته بركعتين خفيفتين.
Muslim narrated it in Prayer of Travelers (767), via Hushaym, who said, "Abu Hurrah told us, from Hasan, from Saad bin Hisham, from Ayesha," and she mentioned the same.