Musannaf Ibn Abi Shayba 3:4045

Abu Bakr narrated to us, he said: Hushaym narrated to us, he said: Yunus bin Ubayd informed us, from Ibn Sirin: That he used to say regarding a man if he enters the mosque while the people are praying the morning prayer: He should enter with the people in their prayer and not pray the two rak'ahs, for what he misses of the obligatory prayer is greater than the two rak'ahs.