'Sustenance is of two kinds. One is the ostensible sustenance and the other is the hidden or spiritual sustenance. The ostensible sustenance relates to food and to other such things, which give nourishment to the body....(the other) implies knowledge, enlightenment and guidance. It is no doubt a better and more superior type of sustenance.'
He further says that as only Allah can give sustenance, emulation of this quality implies reposing trust in Allah alone. It also implies invoking Allah to give knowledge, guidance and a tongue to preach and to proclaim the truth.
He adds that appropriate invocation helps to keep one in affluent circumstances.
see 'The 99 Most Beautiful Names of Allah' by Dr Zahurul Hassan Sharib
Some other references:
Al-Ghazali says of the two kinds of sustenance that the inward is higher since the sustenance of the body lasts only for a while but the fruits of the sustenance of the heart and inmost parts is eternal life. But God is graciously disposed to convey both kinds.
He tells the story of Hatim al-Assam who, when asked from where he ate said "From His storehouse". "Does He hand sustenance down from heaven?" he was then asked. "Were earth not His, He would have to hand it down from heaven" he replied.
"What words you people speak!" his interlocutor exclaimed. "That is because nothing descends from heaven except words" came the response.
Al-Ghazali concludes that to partake of this quality one's hands should be the storehouse of God and one's speech a storehouse of sustenance for hearts.
(Al-Ghazali - The Ninety-nine Beautiful Names of God. Trans. Burrel/Daher: ITS: 1992.)
The one who is given an understanding of this knows in his heart that all things that come to him come from God - both things material and spiritual.
'The world is like a furnace in which different kinds of bread are baked - but he who has seen the Baker Himself, what should he have care for the world?...it is the Baker Who enraptures him. God reveals Himself here under the attribute of ar-Razzaq. He Who bestows the daily bread. Those who love Him, take His gifts only as a means to increase their gratitude.' (The Triumphal Sun: Schimmel.)
Bismillah ir Rehman ir Rahim
The Provider The One Who Provides all Sustenance
Ar-Razzaq (Ar-Razzaaq) Qur'an 51:58 & 42:12
To Him belongs the keys Of the heavens and the earth: He enlarges and restricts The sustenance to whom He will for He knows Full well all things.