Certainty will take the bondsman to every sublime state and every wondrous station; thus did the Messenger of Allah make known the immensity of certainty when he mentioned that ‘Isa (‘a) walked on water. He said, 'If he had had more certainty, he could have walked on air.' By this he indicated that in spite of the majesty of the place which the prophets have with Allah, they also have different ranks according to their certainty. Certainty is ever increasing, and remains so throughout eternity. Believers also vary in the strength and weakness of their certainty. A person whose certainty is strong may be recognised by the fact that he finds himself stripped of all ability and power other than what Allah has given him, and by his keeping to Allah's command and worship both outwardly and inwardly. He considers the states of having and not having, increase and decrease, praise and blame, might and abasement, all to be the same because he considers them all on an equal level. However, a person who weakens his certainty attaches himself to external matters, and allows his self free rein therein. He follows the customs and sayings of people without substantiating them, and strives in the affairs of this world, accumulating its wealth and holding on to it, acknowledging and affirming it with his tongue.
There is no withholder or giver except Allah, and the slave can only obtain what he is provided with and allotted. Effort will not increase provision, but he disavows that by his action and his heart. In Allah's words,
يَقُولُونَ بِأَفْوَاهِهِم مَّا لَيْسَ فِي قُلُوبِهِمْ وَاللّهُ أَعْلَمُ بِمَا يَكْتُمُونَ
Allah was compassionate to His bondsmen when He gave them permission to earn money however they might as long as they do not exceed the limits of Allah or abandon their obligations to Him and the behaviour of His Prophet in any of their actions, or abandon the spirit of trust or become caught in the field of greed. But when they forget this, attaching themselves to the opposite of what has been delineated for them, they are counted among the destroyed, who at the end have nothing but false claims. Not everyone who earns is necessarily trustful: from his earnings he brings for himself only what is forbidden or doubtful. He may be recognized by the effect his gains have upon him, by his insatiable hunger, and how he spends for this world without let.
He who is given permission to earn is one whose self gains while his heart trusts in Allah. If he has a lot of money, he is like a trustee who knows that having property and not having it is the same thing. If he withholds it, he withholds for Allah; and if he spends it, he does so in the way Allah has commanded. Both are for Allah.