四分律行事鈔資持記 1.915

1.915

攝人中。若作師更請者，上四闍梨，必滿十夏，欲從依止；前法已失，故令更請。

In sheltering persons: 'if one acts as master, he should make a request again' means that the four ācāryas above, having certainly completed ten rains, if one wishes to follow them in taking dependance, the previous legal procedure has already been lost; therefore they are ordered to request again.