I cannot count how many times I heard the Messenger of Allah ﷺ recite "Say, O you disbelievers" [Kafirun 109:1] and "Say, He is Allah, the One" [Ikhlas 112:1] in the two units of prayer after Maghrib and in the two units of prayer before Fajr.
حدثنا أبو موسى محمد بن المثنى حدثنا بدل بن المحبر حدثنا عبد الملك بن معدان عن عاصم بن بهدلة عن أبي وائل
ما أحصي ما سمعت من رسول الله ﷺ يقرأ في الركعتين بعد المغرب وفي الركعتين قبل صلاة الفجر بقل يا أيها الكافرون وقل هو الله أحد
Sourcing, its chain is daif. Ibn Majah related it in the Book of Establishing the Prayers, chapter on what is recited in the two rakats after Maghrib, hadith no. 1166, through Badal, with the same wording, and its chain is daif. The hadith has daif corroborating narrations with Nasai, no. 993, and others.On this subject there is also a narration from Ibn Umar [Nasai, no. 993] (per my verification), and its chain is daif. Abu Ishaq did not explicitly state that he heard it, and I did not find any evidence that he does not practice tadlis from Mujahid. Allah knows best. Part of the hadith has a corroborating narration in Muslim, no. 726.