大般涅槃經義記 1.51

1.51

問曰：羅漢已離壞苦，何故悲惱？釋言：羅漢於世法中憂悲已斷，於佛境界不能自裁，故生悲惱。其猶迦葉及阿難等，世間五欲不能傾敗，大樹緊那鼓琉璃琴，摩訶迦葉不覺起舞，阿難比丘不覺歌吟。大樹緊那是其菩薩，上人五欲，小乘不堪，此亦相似。亦可現悲，生眾戀意。

Question: Arhats have already abandoned the suffering of destruction; why would they experience sorrow and distress? Answer: Arhats have already severed grief and sorrow regarding worldly phenomena, but with respect to the Buddha's realm they cannot contain themselves, so they give rise to sorrow and distress. Just as Kāśyapa, Ānanda, and the others could not be overthrown by the five worldly desires, yet when the kinnara king Druma played his lapis lazuli lute, Mahākāśyapa unwittingly stood up and danced, and the monk Ānanda unwittingly began to sing. The kinnara Druma was a bodhisattva; the five desires of superior beings cannot be sustained by the Hīnayāna, and this is similar. Alternatively, they may have manifested grief to arouse feelings of yearning in the assembly.