首楞嚴義疏注經 1.361

1.361

破多也。汝心惟一，豈合言多？若許多心，汝亦多體。多體之內誰為阿難？故云何體為汝。

This refutes 'many.' Your mind is only one; how could one speak of many? If you allow many minds, you would also have many bodies. Among the many bodies, which one would be Ānanda? Hence he says, 'which substance would be you?'