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)
أَنَّ رَسُولَ اللهِ ﷺ قَالَ إِذَا أُقِيمَتِ الصَّلَاةُ فَلَا صَلَاةَ إِلَّا الْمَكْتُوبَةُ