Robert Graves phrases her oracle to Aegeus as follows:
The Oracle warned him not to untie the of mouth his bulging wine-skin until he reached the highest point of Athens, lest he one day die of grief
Many other modern retellings mention dying of grief in the prophecy as well, but I haven't found it in Grave's cited sources
In Euripides' Medea it only says:
AEGEUS: He told me this: “Don’t untie the wineskin’s foot. . .” MEDEA: Until when? Until you do what or reach what country? AEGEUS: “. . .until you come back to your hearth and home.”
No mention that he would die of grief
In Plutarch life of Theseus:
Loose not the wine-skin's jutting neck, great chief of the people, Until thou shalt have come once more to the city of Athens.
No mention that he would die of grief
In Pseudo-Apollodorus:
The bulging mouth of the wineskin, O best of men, loose not until thou hast reached the height of Athens.
No mention that he would die of grief
Wikipedia even attributes the "die of grief" version to Pseudo-Apollodorus and Plutarch Life of Theseus, but as we have established, neither mentioned it in their versions of the prophecy.
The only sources I wasn't able to find in English were the Scholia on Euripides' Medea and Tzetzes on Lycophron, do either of them have the Pythia mention dying of grief in the prophecy?
Does any ancient source say the Pythia warned Aegeus he would die of grief, or is this purely a modern invention?