法華義疏 5.71

5.71

有人言：此舉上之獨行就下之在會，總明兩處失諸勝德耳。有人言：身子不在佛會，但遙見佛在會，故自傷耳。

Some say: this takes the walking alone above and applies it to being in the assembly below, collectively clarifying that he lost these superior virtues in both places. Some say: Śāriputra was not in the Buddha's assembly, but merely saw the Buddha in the assembly from afar, and therefore lamented to himself.