法華論疏 2.412

2.412

問：佛受身子請，誡聽許說。云何乃是身子取授記？答：以身子機緣中欲得受記作佛，受請許說也。

Question: The Buddha accepted Śāriputra's entreaty, admonished him to listen, and consented to speak. How is this Śāriputra obtaining prediction? Answer: Because within Śāriputra's spiritual capacity and condition he wished to obtain prediction of becoming a buddha, the Buddha accepted the entreaty and consented to speak.