نَصَبِ الدُّنْيَا refers to worldly toil and exhaustion. In أَذَاهَا, the pronoun هَا refers to the world: “its hurt or distress.” The first part of the hadith describes the believer’s rest from life’s hardships in Allah’s mercy.
This is not an invitation to abandon worldly duties. Worship, earning a living, care for dependents, and fulfilling obligations are part of life’s responsibilities. Hope for the Hereafter should give strength to endure difficulty and act well, not encourage withdrawal from duty.