´It was narrated from 'Uqbah bin 'Amir that :` He asked the Messenger of Allah [SAW] about Al-Mu'awwidhatain. 'Uqbah said: "The Messenger of Allah [SAW] recited them when he led us in Salah Al-Ghadah (As-Subh)."
Hadith Referenceسنن نسائي / كتاب الاستعاذة / 5436
Hadith Gradingالألبانی:صحيح | زبیر علی زئی:حسن
Hadith Takhrij«انظر حدیث رقم: 953 (صحیح)»
Brief Explanation
1؎ : At that particular time, in order to emphasize the importance of these two surahs specifically, the Prophet (sallallahu alayhi wa sallam) led the prayer reciting only these two surahs. In the Fajr prayer, although he would generally recite long surahs, at times he would also recite medium-length or even short surahs, to the extent that he would sometimes recite the "Mu'awwidhatayn" (the two surahs of seeking refuge, i.e., Surah al-Falaq and Surah an-Nas). All these variations were done according to different circumstances—sometimes due to vigor, and at other times to demonstrate permissibility.
Explanation & Benefits
Hafiz Muhammad Ameen
In the morning prayer (Fajr), reciting at length is Sunnah. This was the practice of the Prophet sallallahu alayhi wa sallam; however, on that day, reciting these two short surahs in the morning prayer was to demonstrate their significance—that despite being brief, they are very comprehensive and virtuous, to the extent that they can suffice in place of lengthy recitation in the morning prayer.
Source: Sunan Nasa'i: Translation and Benefits by Shaykh Hafiz Muhammad Amin Hafizullah, Page: 5436