俱舍論疏 14.150

14.150

論「以經復說至令識堅持」，重引餘經證。以經自稱我是近事，後復說我從今時乃至命終捨生言故，故知前時已得五戒。彼雖已得，令了知故，為說捨生等五種戒相令識堅持。

The commentary states: "Because the sūtra furthermore states [...] causing them to understand and firmly uphold [them]", which again cites another sūtra as proof. Because the sūtra says that having personally proclaimed 'I am an upāsaka', one furthermore utters the words 'from this time onward until the end of my life I abandon killing living beings', therefore we know that previously one had already obtained the five precepts. Although they have already been obtained, in order to make them understood, the five precept characteristics such as abandoning killing living beings are spoken for him to cause him to understand and firmly uphold them.