四分律行事鈔資持記 1.76

1.76

《高僧傳》論云：上座大眾，創分結集之場；彼言大眾，乃是窟外；此云大眾，定是窟內，即今《摩訶僧祇》。此翻大眾，以五百人亦大眾故（《智論》則云千人）。是則大眾名通二部，上座唯局窟內，學者須細辨之。一家者，且據五部各自為言。

The treatise in the Biographies of Eminent Monks says: "The Sthaviras and the Mahāsāṃghikas first divided the grounds of the compilation." Its mention of the Mahāsāṃghikas refers to those outside the cave; the mention of the Mahāsāṃghikas here definitely refers to those inside the cave, which is the present Mahāsāṃghika-vinaya. This is translated as "Great Assembly" because five hundred people are also a great assembly (the Mahāprajñāpāramitopadeśa, however, says a thousand people). Thus, the name "Great Assembly" applies to both groups, while "Sthavira" is confined solely to those inside the cave; students must distinguish this carefully. "A single lineage" is said provisionally with each of the five schools speaking for itself.