法華義疏 5.45

5.45

此言初聞者，不云身子在眾人之初。但身子本學外道，初從頞鞞始聞佛道即證初果，鬢髮墮落便成沙門。

Saying that he 'heard it first' does not mean that Śāriputra was the first among all people. It merely means that Śāriputra originally studied non-Buddhist teachings, and upon first hearing the Buddha's Way from Aśvajit, he immediately realized the first fruit, his hair and beard fell away, and he became a śramaṇa.