Those who said: he prays four if he finds them sitting

Sa'id bin al-Musayyib, Sayyiduna Anas (may Allah be pleased with him) and al-Hasan said: Whoever catches one rak'ah of the Jumu'ah should add one more rak'ah to it, and if he finds the people sitting in the final sitting of the Jumu'ah prayer, he should pray four rak'ahs.

Alqamah and al-Aswad said: If one finds the people sitting in the final sitting of the Jumu'ah prayer, he should pray four rak'ahs.

Al-Sha'bi was asked: If a person finds the people sitting in the final sitting of the Jumu'ah prayer, what should he do? He said: He should pray four rak'ahs.

Al-Hasan said: If one finds the people sitting in the final sitting of the Jumu'ah prayer, he should pray four rak'ahs.

Sayyiduna Anas bin Malik (may Allah be pleased with him) said: If one finds the people sitting in the final sitting of the Jumu'ah prayer, he should pray four rak'ahs.

Something similar is reported from Sa'id (bin al-Musayyib), Khilas and al-Hasan.

Something similar is reported from Ibrahim.