The phrase "a source of sustenance" is correct and usable in written English.
You can use it to refer to something that gives or provides sustenance, or what sustains a life-form. For example, "The farmer's irrigated land was a source of sustenance for the village."
For them, Mr. Shajahan was a source of sustenance.
Sheep are not only a source of sustenance in Kyrgyzstan but also sacred creatures that were for centuries at the center of tribal life.
Probably more useful as a weapon than as a source of sustenance, it is hard in texture and soul-destroying in taste.
And not one of the many reports about or from the monotowns that I have read so much has mentioned unemployment benefits as a source of sustenance.
"The story of creation in the book of Genesis tells us of trees that are beautiful to behold and a source of sustenance.
Racing was a source of sustenance to Chamberlin when, seven years ago at the age of 35, he was treated for stomach cancer and found himself stuck in hospital during the Cheltenham Festival.
One letter in particular became a source of fascination, sustenance and succour for my grieving father and me.
At the same time, he wishes to prohibit perhaps the world's best-selling book after the Bible and a source of spiritual sustenance for hundreds of millions of Muslims around the world.
I see it as a source of life, of sustenance". The project, he adds, isn't about claiming land as a belonging but instead a way of saying, "I belong here". Within the context of the whitebox gallery, that message will be even more powerful.
Numerous sea birds owe their prosperity to the seasonal appearance of horseshoe crab eggs, a vital source of sustenance at a midway point for migrations from South America to Arctic nesting sites.
Such knowledge is very important in tropical Africa where rain-fed agriculture is a major source of sustenance for a majority of the population.
