大方廣佛華嚴經隨疏演義鈔 63.34

63.34

疏「若琴絃之緩急」者，此是如來教守樓那。彼是大富長者之子，足不履地。出家之後，精勤修道，足下血流。佛問：「汝曾鼓琴耶？」答云：「曾鼓。」「絃緩如何？」答云：「不鳴。」「絃急如何？」答云：「即絕。」「當如何可？」答云：「不緩不急。」佛誨之言：「修道亦爾。」

On the commentary's "like the tightness or looseness of lute strings": this is the Tathāgata instructing Śroṇa. He was the son of an extremely wealthy householder whose feet never touched the ground. After leaving the household life, he cultivated the Path with diligent vigor until his soles bled. The Buddha asked: "Did you ever play the lute?" He answered: "I played it." "When the strings were loose, how was it?" He answered: "It made no sound." "When the strings were tight, how was it?" He answered: "They snapped." "How should they be?" He answered: "Neither loose nor tight." The Buddha instructed him, saying: "Cultivating the Path is just like that."