The Prophet ﷺ used to recite "Say, O you disbelievers" [Kafirun 109:1] and "Say, He is Allah, the One" [Ikhlas 112:1] in the two rakahs after the Maghrib prayer.
حدثنا أحمد بن الأزهر حدثنا عبد الرحمن بن واقد ح و حدثنا محمد بن المؤمل بن الصباح حدثنا بدل بن المحبر قالا حدثنا عبد الملك بن الوليد حدثنا عاصم بن بهدلة عن زر وأبي وائل
أن النبي ﷺ كان يقرأ في الركعتين بعد صلاة المغرب قل يا أيها الكافرون وقل هو الله أحد
[Its chain of transmission is daif] Tirmidhi narrated it in the book of Prayer, chapter on what has been said about the two rakahs after Maghrib and the recitation in them, hadith 431, from the hadith of Badal, through him, in abridged form. Abdul-Malik is daif, as stated in Taqrib and elsewhere. The hadith has daif corroborating narrations in Nasai, hadith 993, and elsewhere.