The Messenger of Allah ﷺ recited in the two rakahs before Fajr and the two rakahs after Maghrib, on more than twenty or more than ten occasions, "Say, O you disbelievers" [Kafirun 109:1] and "Say, He is Allah, the One" [Ikhlas 112:1].
حدثنا وكيع حدثنا إسرائيل عن أبي إسحاق عن مجاهد
أن رسول الله ﷺ قرأ في الركعتين قبل الفجر والركعتين بعد المغرب بضعا وعشرين مرة أو بضع عشرة مرة قل يا أيها الكافرون و قل هو الله أحد
Its isnad is sahih. Abu Ishaq is Subayi.Tirmidhi related only the portion of this hadith about the recitation in the two rakahs before Fajr (1:320-321), through the route of Abu Ahmad Zubayri, from Thawri, from Abu Ishaq, and he said, a hasan hadith. We do not know it from the hadith of Thawri from Abu Ishaq except through the hadith of Abu Ahmad, and what is known among the people is the hadith of Israil from Abu Ishaq. However, Abdul-Razzaq also related it from Thawri from Abu Ishaq, as in 4909, and this hadith has also been related from Abu Ahmad from Israil. It appears in al-Muntaqa, 1168, with the wording of Tirmidhi, and it has also been attributed to Abu Dawud and Ibn Majah.