The Prophet ﷺ said, "When the prayer has been called to begin, there is no prayer except the obligatory one."
عن النبي ﷺ قال: إذا أقيمت الصلاة، فلا صلاة إلا المكتوبة.
Muslim narrated it in the Book of the Prayer of Travelers (710), from Ahmad bin Hanbal, who said, Muhammad bin Jafar told us, Shuba told us, from Warqa, from Amr bin Dinar, from Ata bin Yasar, from Abu Hurairah, who said, and then he related it. Muslim also narrated it through Hammad bin Zayd, from Ayub, from Amr bin Dinar, in the same manner. Hammad said, "Then I met Amr, and he related it to me without raising it to the Prophet." End of quote.I say, Sufyan bin Uyayna likewise narrated it from Amr bin Dinar without raising it. Tirmidhi said, "The narration that is raised to the Prophet is more sahih in our view." Baghawi likewise favored the raised narration in Sharh al-Sunnah (3/362), as did Nawawi in Sharh Muslim, and Bayhaqi, and others, because the raised version contains an addition, and such additions are accepted by the majority of scholars.As for what has been reported regarding the exception of the two rakahs of Fajr, the chain of transmission includes Hajjaj bin Nasr, from Abbad bin Kathir, from Layth, and all of them are daif narrators. This is discussed in detail in Minna Kubra (2/310).