法華義疏 1.237

1.237

「孫陀羅難陀」者，此是佛弟難陀，是大愛道所生，身長一丈五尺二寸，佛到迦毘羅城二日即度之。孫陀羅者，此云端正亦云柔軟，欲異前者故以婦標名焉。

Regarding "Sundarananda": this was the Buddha's younger brother Nanda, born of Mahāprajāpatī. His body was one *zhang*, five *chi*, and two *cun* tall; two days after the Buddha arrived at the city of Kapilavastu, he delivered him. "Sundara" is translated here as "upright and handsome," and also as "soft and supple"; wishing to distinguish him from the former one, he was designated by his wife's name.