Sunan al-Shafi'i

And Umm Karz says: I also heard the Prophet ﷺ say, "Let the birds remain in their nests." Imam Shafi’i, may Allah have mercy on him, says that the meaning of the statement of the Prophet of Allah صلى الله عليه وسلم, "Let the birds remain in their nests," is that the knowledge of the Arabs was to make birds fly, to estimate their direction (right or left), to draw lines, and to scold the birds. When an Arab would leave his house for some task, he would first look at a bird. If the bird flew to the right instead of the left, the Arab would say, "This is a right-sided bird," and would proceed with his task, believing he would be successful. If the bird passed to the left instead of the right, he would consider it an unlucky bird and would abandon his journey, thinking it was a bad omen. Hatika the poet praised Abu Musa Ash’ari, may Allah be pleased with him, saying: "When he goes for any task, he does not take bad omens by making birds fly, nor does he draw or throw arrows of fate. That is, according to the Islamic way, he relies on Allah Almighty and has abandoned the ignorant custom of taking omens from birds." Some Arab poets praised themselves in this way: "I am not among those who make birds fly for their purposes (I do not refrain from my objectives) whether a crow or a fox appears before me." If an Arab did not find a bird on the way, he would go and make one fly from its nest to find out whether the path would be unlucky or peaceful. This is the meaning of the statement of the Prophet Muhammad صلى الله عليه وسلم: "Let the birds remain in their nests, do not disturb them." There is no effect or power in the movement of birds; everything happens by the decree of Allah Almighty.