It is narrated from Sayyiduna Jabir bin Abdullah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said while delivering the sermon: "When one of you comes on Friday while the imam is delivering the sermon, or has already come out, let him pray two rak'ahs."
Hadith Referenceالمعجم الكبير للطبراني / باب السين / 6671