佛說盂蘭盆經疏 2.80

2.80

說此語時，亦是設供之後，非一席之事。至畢鉢羅窟，方始總集為經也。目連愛其親而及他人，如潁考叔諫莊公也。

When these words were spoken, it was also after the offering had been set out; it did not happen on a single occasion. It was only when they reached the Pippala Cave that it was first compiled into a sūtra. Maudgalyāyana cared for his own parents and extended it to others, just as Ying Kaoshu admonished Duke Zhuang.