The masjid of the tribe of Banu Salama in Madinah. Its congregation was praying Asr when a companion arrived with news that the qibla had changed to Makkah, and the entire jama'ah turned mid-prayer, with the imam walking through the rows to the new front.
Became known as "the Mosque of the Two Qiblas" because its congregation, uniquely, physically turned direction mid-salah upon hearing the news, unlike the Prophet ﷺ's own masjid, where the change was announced between prayers, not during one.