When. Not a supplication in form — these are transmitted words about reliance, and they are recalled at the moment provision looks uncertain: a contract that did not renew, a month with the arithmetic not working.
The words. Tawakkul comes from the root w-k-l, the root of wakil, an agent appointed to act on your behalf. To rely on Allah is, in the language, to appoint Him as the one who handles the matter. The phrase haqqa tawakkulih — "with the truth of reliance upon Him" — sets the condition and admits, by stating it, that most reliance is not that.
The birds. The comparison is exact, and it is usually misread. A bird is described as going out hungry in the morning and returning full — it goes out. Nothing in the image shows a creature waiting. The birds work all day for what they get, and it arrives; reliance is placed on the outcome, not on the effort being unnecessary.
Why this correction is needed. Reliance is the doctrine most easily bent into passivity, and this is the clearest statement against that reading. It uses an animal precisely because animals have no capital, no savings and no contracts, and still do not sit still.
What it does not say. There is no promise of wealth in it, and no schedule. Birds are fed; they are not fed abundantly, and some days they are not fed at all.
Its companion. The requests for provision found elsewhere are the asking half. This is the disposition a person is meant to hold while asking.