5.

Book of Friday

٥-
‌كِتَابُ الْجُمُعَةِ

Who said if he catches them sitting, he prays four rak'ahs

‌مَنْ قَالَ: يُصَلِّي أَرْبَعًا إِذَا أَدْرَكَهُمْ جُلُوسًا

Musannaf Ibn Abi Shaybah 5352