وَمَنْ أَدْرَكَ الْإِمَامَ يَوْمَ الْجُمُعَةِ: صَلَّى مَعَهُ مَا أَدْرَكَ، وَبَنَى عَلَيْهَا الْجُمُعَةَ.
Translation: Whoever joins the imam during Friday prayer performs the part reached and completes Jumuah on that basis.
“Catching Jumuah” determines whether the latecomer completes the two Friday rak‘ahs or must instead perform four rak‘ahs of Zuhr. The next rule states the disputed cutoff.