I think that I have found the source of that quotation. It is from: What the Buddha
Taught, by Walpola Rahula.
"When the Aggregates arise, decay and die, O Bhikkhu, every moment you are born, decay
and die." (note 1) [from page 33.]
"Note 1. Prmj.I(PTS), p.78.'Khandhesu jayamanesu jiyamanesu miyamanesu ca khane khane
tvam bhikkhu jayase ca jiyase ca miyase ca.' This is quoted in the Paramatthajotika
Commentary as the Buddha's own words. So far I have not been able to trace this passage
back to its original text."