(9) باب كَرَاهَةِ الشُّرُوعِ فِي نَافِلَةٍ بَعْدَ شُرُوعِ الْمُؤَذِّنِ
Abu Huraira reported the Messenger of Allah (ﷺ) as saying:
When the prayer commences then there is no prayer (valid), but the obligatory prayer. This hadith has been narrated by Warqa' with the same chain of transmitters. (ID)
Reference (ID): Sahih Muslim 710 a (ID)
In-book reference (ID): Book 6, Hadith 75 (ID)
USC-MSA web (English) reference(deprecated numbering scheme): Book 4, Hadith 1531 (ID)