The Messenger of Allah ﷺas saying: When the iqamah is pronounced for prayer, no prayer is valid except the obligatory prayer. (Using translation from Abū Dāʾūd 1266)  

قَالَ رَسُولُ اللهِ ﷺ «إِذَا أُقِيمَتِ الصَّلَاةُ فَلَا صَلَاةَ إِلَّا الْمَكْتُوبَةَ»  

The Messenger of Allah ﷺas saying: When the iqamah is pronounced for prayer, no prayer is valid except the obligatory prayer. (Using translation from Abū Dāʾūd 1266)  

عَنِ النَّبِيِّ ﷺ قَالَ «إِذَا أُقِيمَتِ الصَّلَاةُ فَلَا صَلَاةَ إِلَّا الْمَكْتُوبَةَ»  

[Machine] The Fajr prayer was established, and the Messenger of Allah ﷺ saw a man praying while the muezzin was calling the prayer. He said, "Are you praying Fajr four times?" (Hadith 942) And it was narrated by Mahmoud bin Ghailan, from Wahb bin Jarir, from Shu'bah, from Saad bin Ibrahim, from Hafs bin Asim with it.  

أُقِيمَتْ صَلَاةُ الصُّبْحِ فَرَأَى رَسُولُ اللهِ ﷺ رَجُلًا يُصَلِّي وَالْمُؤَذِّنُ يُقِيمُ فَقَالَ «أَتُصَلِّي الصُّبْحَ أَرْبَعًا؟» 942 وَعَنْ مَحْمُودَ بْنِ غَيْلَانَ عَنْ وَهْبِ بْنِ جَرِيرٍ عَنْ شُعْبَةَ عَنْ سَعْدِ بْنِ إِبْرَاهِيمَ عَنْ حَفْصِ بْنِ عَاصِمٍ بِهِ