(46) باب فِي الصَّلاَةِ تُقَامُ وَلَمْ يَأْتِ الإِمَامُ يَنْتَظِرُونَهُ قُعُودًا
Abu al-Nadr said:
when the Iqamah was pronounced and the Messenger of Allah (ﷺ) saw that they (the people) were small in number, he would sit down, nd would not pray; but when he saw them (the people) large in number, he would pray.
Reference: Sunan Abi Dawud 545
In-book reference: Book 2, Hadith 155
English translation: Book 2, Hadith 545