PONOS (or Ponus) was the spirit (daimon) of hard labour and toil. (N.B. Extreme physical labour is implied rather than just hard work--for example, the labour required of subsistence farmers just to survive.)

Hesiod, Theogony 226 ff (trans. Evelyn-White) (Greek epic C8th or C7th B.C.) :
"But abhorred Eris (Strife) bare painful Ponos (Toil), and Lethe (Forgetfulness), and Limos (Starvation), and the Algea (Pains), full of weeping, the Hysminai (Fightings) and the Makhai (Battles), the Phonoi (Murders) and the Androktasiai (Man-slaughters), the Neikea (Quarrels), the Pseudo-Logoi (Lies), the Amphillogiai (Disputes), and Dysnomia (Lawlessness) and Ate (Ruin), who share one another's natures, and Horkos (Oath)."

Cicero, De Natura Deorum 3. 17 (trans. Rackham) (Roman rhetorician C1st B.C.) :
"Their [Aether and Hemera's] brothers and sisters, whom the ancient genealogists name Amor (Love), Dolus (Guile), Metus (Fear), Labor (Toil) [Ponos], Invidentia (Envy), Fatum (Fate), Senectus (Old Age), Mors (Death), Tenebrae (Darkness), Miseria (Misery), Querella (Complaint), Gratia (Favour), Fraus (Fraud), Pertinacia (Obstinacy), the Parcae (Fates), the Hesperides, the Somnia (Dreams) : all of these are fabled to be the children of Erebus (Darkness) and Nox (Night)."

Seneca, Oedipus 647 ff (trans. Miller) (Roman tragedy C1st A.D.) :
“[The ghost of Laius demands Oidipous be expelled from Thebes before he will summon back to Haides the pestilent daimones which ravage the land ;] `Wherefore speedily expel ye the king from out your borders, in exile drive him to any place so-ever with his baleful step. Let him leave the land; then, blooming with flowers of spring, shall it renew its verdure, the life-giving air shall give pure breath again, and their beauty shall come back to the woods; Letum [Ker, ruin] and Lues [Ker or Nosos, pestilence], Mors [Thanatos, death], Labor [Ponos, hardship], Tabes [Phthisis, corruption] and Dolor [Algos, distress], fit company for him, shall all depart together. And he himself with hastening steps shall long to flee our kingdom, but I will set wearisome delays before his feet and hold him back. He shall creep, uncertain of his way, with the staff of age groping out his gloomy way. Rob ye him of the earth; his father will take from him the sky.'"

Statius, Thebaid 10. 90 ff (trans. Mozley) (Roman epic C1st A.D.) :
"Within [the halls of Somnus or Hypnos god of sleep], glowing Mulciber [Hephaistos] had carved a thousand likenesses of the god [Hypnos] : . . . here [on one wall] Labor (Labour) [Ponos] drooping to repose bears him company."

Sources:

• Hesiod, Theogony - Greek Epic C8th-7th B.C.
• Cicero, De Natura Deorum - Latin Rhetoric C1st B.C.
• Seneca, Oedipus - Latin Tragedy C1st A.D.
• Statius, Thebaid - Latin Epic C1st A.D.