That story appears in one of the most beautifully written stories that can exist. In Herodotus Histories, chapter 1.
The Athenian lawgiver Solon is visiting the richest man in the world
the Lydian Croesus and Croesus want to impress Solon and show him how
rich and wealthy he is and after asks him who is the happiest
My Athenian guest, [...] I really can't resist asking you now
whether you have yet seen anyone who surpass all others in happiness
Solon tries to give a very polite answer to Croesus telling him the story of the Athenian Tellus who died bravely defending Athens and was honored for that. Obviously, Croesus insists a little bit asking for a second person and here is your story in its full glory.
Cleobis and Biton. The were Argives [inhabitant of Argos] who had
enough resources to live on and in addition were physically fit, as in
shown by the fact that they both won prizes at athletics contests, as
well as by this story told about them.
The Argives were having a festival for Hera, and their mother had to be taken to the shrine in a wagon, but the oxen were not back from the fields in time to pull it. [...] The young men put themselves under the yoke and themselves hauled the wagon.[...] their mother was simply elated by her sons' feat and by all the praise [from the Argives' crowd]. She stood before the statue of the goddess and said a prayer for [them]: that since they had shown her such great honour let the goddess grant them the best thing human being could have. [After the fest], the young men fell asleep in tat very sanctuary and never awake again. [showing clearly that it is better for a human being to be dead than to be alive]
Translation from the Landmark Herodotus.
Solon will explain then to him than no one can be called happy until his life is over. Pissed off Croesus sent Solon away. Later on, he will defy the Persian Lord Cyrius the Great and be beaten.
In Plutarch's Parallel lives
You find this story retold in Plutarch's Parallel lives in the Solon chapter (his roman par is Publius Valerius, Poplicola):
Yes, Cleobis and Biton, who were loving brothers, and extremely
dutiful sons to their mother, and, when the oxen delayed her,
harnessed themselves to the wagon, and drew her to Juno's temple, her
neighbors all calling her happy, and she herself rejoicing; then,
after sacrificing and feasting, they went to rest, and never rose
again, but died in the midst of their honor a painless and tranquil
I don't think you find that story in Ovid.
The landmark Herodotus
Parallel lives by Plutarch I have no advice in English edition. Unfortunately, I read other languages with so good translations...
Metamorphoses by Ovid