Ibrahim bin Mahmud (may Allah have mercy on him) said: Someone asked Yunus bin Abd al-A'la (may Allah have mercy on him) what is meant by the saying of the Prophet (peace and blessings be upon him): "Leave the birds in their places." He said: Allah loves the truth. Imam al-Shafi'i (may Allah have mercy on him) explained it as follows: In the Jahiliyyah, when a person had some task to do, he would make the birds fly from their nests. If a bird flew to the right, he would go ahead with his task, and if it flew to the left, he would refrain from it. So the Messenger of Allah (peace and blessings be upon him) forbade this.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الضحايا / 19338