´It was narrated from ‘Abdullah bin Mas’ud that for the two Rak’ah after Maghrib, the Prophet (ﷺ) used to recite:` “Say: O you disbelievers!” [Al-Kafirun (109)] and “Say: He is Allah the One.” [Al- Ikhlas (112)]
Hadith Referenceسنن ابن ماجه / كتاب إقامة الصلاة والسنة / 1166
Hadith Takhrij« حدیث زرعن عبد اللہ مسعود تفرد بہ ابن ماجہ ، ( تحفة الأشراف : 926 ) وحدیث أبي وائل عن ابن سعود : أخرجہ : سنن الترمذی/الصلاة 204 ( 431 ) ، ( تحفة الأشراف : 9278 ) ( ضعیف ) » ( اس کی سند میں بدل بن المحبر اور عبد الملک بن الو لید ضعیف ہیں ، ملاحظہ ہو : المشکاة : 851 )
´Abdullah bin Mas'ud narrated:` "I can not enumerate (how many times) I heard Allah's Messenger (S) reciting - in the two Rak'ah after Al-Maghrib and the two Rak'ah before Salatul-Fajr with: Say: "O you disbelievers!" and Say: "He is Allah the One."
Shaykh Dr. Abdur Rahman Freywai
1⎋: This hadith indicates that it is recommended (mustahabb) to recite these two surahs in the two sunnah rak‘ahs of Maghrib.
Source: Sunan al-Tirmidhi – Majlis ‘Ilmi Dar al-Da‘wah, New Delhi Edition, Page: 431