Tafsir of Al-Feel 105:3

(And He sent against them birds in flocks [Ababil]), meaning groups. It is the plural of ibalah—with a kasra on the hamza and a tashdid on the ba—though al-Farra’ narrated ibalah with a light [un-doubled] ba. It is a large bundle of firewood, and the groups of birds were likened to it due to their cohesion; it is also used for other things, as in the poet’s saying: “My riding beast was nearly toppled by the sounds, as the earth was filled with swarms [ababil] of horses.”

It is said that its singular is abul, like ‘ajul and ‘aqil, or abil, like sikkin; it is also said to be abala. Abu Ubaydah and al-Farra’ said: It has no singular from its own root, like ‘ababid—which refers to groups of people going in every direction—and shamamit, which are scattered pieces.

These birds came—as narrated by a group from the direction of the sea. They were neither Najdi, nor Tihami, nor Hijazi. Some have claimed that the pigeons of the Sanctuary are of their offspring, but that is not authentic. Similarly, what is reported in Hayat al-Hayawan—that they nest and hatch between the heaven and the earth—is likewise. The difference of opinion regarding their color has already been mentioned. It is narrated from ‘Ikrimah: “It was as if their faces were like the faces of beasts of prey; they had never been seen before that, nor after it.”