The root of all suffering is attachment.
This is a saying from the Pali canon, upadhi dukkhassa mūlanti, which means “Attachment is the root of suffering.” So this is a genuine canonical quote.
You’ll find it in this sutta, but translated by Thanissaro as “Acquisition is the root of stress.” His translations are rather idiosyncratic.
In this translation of the same sutta it’s “acquisition is the root of suffering.”
Bhikkhu Bodhi’s translation (not available online, but in The Middle Length Discourses of the Buddha, page 868) has “attachment is the root of suffering,” although he sometimes has “acquisition” in place of “attachment,” in various repetitions of the phrase.