If someone arrives for Jumu'ah while the imam is giving the khutbah, he should pray two rak'ahs

Hazrat Jabir narrates that once the Holy Prophet (peace and blessings be upon him) was delivering the Friday sermon when Sulaik Ghatafani arrived. The Holy Prophet (peace and blessings be upon him) said to him, "Perform two short rak'ahs."

Hasan narrates that once the Prophet Muhammad (peace and blessings be upon him) was delivering the Friday sermon when Sulaik Ghatafani arrived; he had not performed two rak'ahs. The Prophet Muhammad (peace and blessings be upon him) instructed him to perform two short rak'ahs.

Hazrat Muhammad bin Qais narrates that when the Holy Prophet (peace and blessings of Allah be upon him) instructed him to perform two rak'ahs, he paused the sermon. When he finished the two rak'ahs, the Prophet resumed the sermon.

Hazrat Hammad bin Abi Darda says that when the Imam was delivering the sermon, Hasan used to perform two rak'ahs.

Ibn Aun states that if Hasan entered the mosque during the Imam's sermon, he would perform two rak'ahs.

Hazrat Abu Majliz says that when the Imam is delivering the sermon and you enter the mosque, if you wish, you may perform two rak'ahs, and if you wish, you may sit down.