Trust in God (tawakkul) is like the bird that leaves its nest hungry and returns full
Al-Ghazali is careful to note the bird in this hadith still leaves the nest and searches for food, using that detail to argue that real trust in God concerns the heart's inner posture, not the abandonment of ordinary effort.
The hadith, cited by al-Ghazali in Book 35 of the Ihya, his book devoted specifically to tawakkul, pictures a bird leaving its nest each morning hungry and returning each evening with its stomach full, a detail al-Ghazali will not let readers skip past, because the bird does not wait in the nest for food to arrive, it goes out and searches. He uses this to correct a misunderstanding common among ascetics of his own time, who took trust in God as license to abandon ordinary effort, work, provision, even medicine, altogether. His actual position, laid out at length in Book 35, is that trust concerns the heart's inner state toward outcomes, not the abandonment of outward causes, so a person practicing real tawakkul still acts and plans, but without the anxious grasping that assumes results depend on one's own effort alone.
They go out hungry in the morning and come back full in the evening.
Ihya Ulum al-Din