“Lawful” concerns more than the job title or source of money; the method, truthfulness, and others’ rights also matter.
1. Completing agreed work for a fair wage illustrates honest earning.
2. Concealing a defect in goods to secure payment contradicts integrity.
3. Deliberately neglecting an agreed duty while demanding full wages can raise a question of others’ rights.
كَسْب concerns earning; حلال describes the requirement that this earning be permissible. The narration directs attention to the lawful manner of gaining income, not merely its size.