Allah's Messenger (ﷺ) said: "Whoever is in time for a Rak'ah of the Friday prayer, or any other prayer, should add another (Rak'ah) to it and his prayer will then be complete."[an-Nasa'i, Ibn Majah and ad-Daraqutni reported it; the wording is from ad-Daraqutni. Its chain of narrators is Sahih (authentic), but Abu Hatim strengthened the view that it is Mursal (missing link after the Tabi'i)].