首楞嚴義疏注經 5.325

5.325

優波離，云近執，即如來為太子時親近執事之臣也。在家執事，出家亦爾，遂見修行降魔制外，斷惑成道也。故承如來教以持戒，律中度諸釋種，先度波離者，蓋以初雖隨佛，後方得度。

Upāli is translated as 'close attendant', being the servant who closely attended the Tathāgata when he was a prince. Serving as an attendant in domestic life, he did likewise upon renouncing home, and thus witnessed the cultivation, the subduing of maras and mastering of non-Buddhists, the cutting off of delusions, and the attainment of the Way. Therefore, he received the Tathāgata's teaching on maintaining the precepts. In the Vinaya, among the Śākya clan members delivered, Upāli was delivered first because, although he followed the Buddha from the beginning, only later did he obtain ordination.