Umar Ibn Muslim was one of the companions of Imam Sadiq (a.s) and used to visit him (a.s) frequently.
Once, when he did not visit the Imam (a.s) for a long time, he (a.s) inquired about him from ‘Ali Ibn Abdul Aziz, who said: “May I be made your ransom! He has stopped working for his livelihood, and has engaged himself in worship and asceticism instead. Hearing this, Imam Sadiq (a.s) said: “Woe unto him! But does he not know that the prayers of one, who stops working, go unanswered!” During the time of the Noble Prophet (s.a.w), when the verse:
وَ مَنْ يَتَّقِ اللٌّهَ يَجْعَلْ لَهُ مَخْرَجاً وَ يَرْزُقْهُ مِنْ حَيْثُ لا يَحْتَسِبُ
“And whoever is careful of (his duty to) Allah, He will make for him an outlet, and give him sustenance from whence he thinks not”7 was revealed, a group from amongst the Muslims abandoned their professions, adopted seclusion and engaged themselves in worship, saying: “Allah Himself provides the sustenance and shall never permit the religious ones to become distressed and destitute; hence why do we need to toil in order to procure our sustenance.”
When the Noble Prophet (s.a.w) was informed of this, he (s.a.w) summoned them and objecting at this attitude of theirs, asked: “Why have you abandoned your professions?” They replied: “Allah has undertaken to provide us our sustenance.” When he (s.a.w) heard this, he explained: “It is not as you think. Allah does not answer the prayers of a person who, despite possessing the ability to work and exert himself, fails to do so. You must continue to engage yourselves in your respective professions.”( Ba Mardum In Guneh Barkhord Konim, pg. 163; al-Wafi, vol. 10, pg. 15 )