SB 3.1.8

dyūte tv adharmeṇa jitasya sādhoḥ
 satyāvalambasya vanaṁ gatasya
na yācato ’dāt samayena dāyaṁ
 tamo-juṣāṇo yad ajāta-śatroḥ
Synonyms: 
dyūte — by means of gambling; tu — but; adharmeṇa — by unfair tricks; jitasya — of the vanquished; sādhoḥ — a saintly person; satya-avalambasya — one who embraced truth as shelter; vanam — forest; gatasya — of the goer; na — never; yācataḥ — when asked for; adāt — delivered; samayena — in due course; dāyam — right share; tamaḥ-juṣāṇaḥ — overwhelmed by illusion; yat — as much as; ajāta-śatroḥ — of one who had no enemy.
Translation: 
Yudhiṣṭhira, who was born without any enemy, was unfairly defeated in gambling. But because he had taken the vow of truthfulness, he went off to the forest. When he came back in due course and begged the return of his rightful share of the kingdom, he was refused by Dhṛtarāṣṭra, who was overwhelmed by illusion.
Purport: 

Mahārāja Yudhiṣṭhira was the rightful heir to his father’s kingdom. But just to favor his own sons, headed by Duryodhana, Dhṛtarāṣṭra, Mahārāja Yudhiṣṭhira’s uncle, adopted various unfair means to cheat his nephews of their rightful share of the kingdom. At last the Pāṇḍavas demanded only five villages, one for each of the five brothers, but that was also refused by the usurpers. This incident led to the War of Kurukṣetra. The Battle of Kurukṣetra, therefore, was induced by the Kurus, and not the Pāṇḍavas.

As kṣatriyas, the proper livelihood of the Pāṇḍavas was only to rule, and not to accept any other occupation. A brāhmaṇa, kṣatriya or vaiśya will not accept employment for his livelihood under any circumstances.