Ayesha was asked about the two units of prayer before the dawn prayer. She said, "The Messenger of Allah ﷺ used to keep them brief." She added, "I think he used to recite something like 'Say, O disbelievers' and 'Say, He is Allah, the One.'"
حدثنا عبد الوهاب الثقفي عن أيوب
أن عائشة سئلت عن ركعتي الفجر فقالت كان رسول الله ﷺ يخففهما قالت فأظنه كان يقرأ بنحو من قل يا أيها الكافرون وقل هو الله أحد
Its chain of transmission is sahih. It was narrated by Muslim, 1/502, no. 726, in "Travelers," by Abu Dawud, 2/19, no. 1256, in "Voluntary Prayers," and by Nasai, 2/155, no. 945, but all of them from Abu Hurairah, and by Tirmidhi, 2/276, no. 417, and Ibn Majah, 1/363, no. 1149.