Tafsir of Al-Feel 105:4

(Striking them with stones) is another adjective describing the "birds," and the present tense is used to depict the scene and evoke that wondrous image. Abu, Abu Ya'mar, Isa, and Talha (in one narration) read it as yarmihim (striking them) with a ya at the beginning; the hidden pronoun refers to the birds as well. The masculine gender is used because [the word tayr] is a collective noun, which, according to what al-Khafaji recounted, requires the masculine; its feminine usage is due to an interpretation of it as "a group." It is said that both forms are permissible, which is the evident view of Abu Hayyan. It is also said that the pronoun refers back to "your Lord," but that is not the preferred view. The aforementioned reading is attributed to Abu Hanifah (may Allah the Exalted be pleased with him), as recounted in al-Bahr. However, the author of an-Nashr states that he (may Allah be pleased with him) has no [specific] reading, and that the readings attributed to him are fabricated.

(Of Sijjil) is an adjective for "stones," meaning consisting of petrified clay; it is an Arabized form of sang-i-gil (Persian for "clay-stone"). It is said to be purely Arabic, derived from al-sijill (with a kasra), which is a large water bucket. The meaning of the stones being "of the bucket" is that they were successive and numerous, like water poured from a bucket; thus, it contains a metaphorical and imaginative trope. It is also said to be from al-isjal, meaning "sending forth," implying stones that were sent forth. In all these cases, the particle min (of/from) indicates the origin. Others say it is from as-sijill, meaning "the register," taken from as-sijjin, and used as a proper name for the record in which the punishment of the disbelievers was inscribed; here, the meaning would be "from among the punishment written and recorded," making the min partitive.

There is disagreement regarding the size of the birds and the size of those stones. It has been said that [the birds] were like swallows and the stones like chickpeas and lentils. Abu Nu'aym narrated from Nawfal ibn Abi Mu'awiyah al-Daylami that he said: "I saw the pebbles with which the People of the Elephant were struck; they were pebbles like chickpeas, larger than lentils, reddish-black, as if they were beads from Dhofar." Abu Nu'aym also narrated in ad-Dala'il from Ibn Abbas that he said: "Stones like hazelnuts," and in a narration by Ibn Marduyah from him: "Like sheep droppings." 'Abd ibn Humayd, Ibn Jarir, and Ibn Abi Hatim narrated from 'Ubayd ibn 'Umayr that he said regarding this verse: "They were birds that emerged from the direction of the sea, resembling the men of Sindh, carrying stones like kneeling camels—or the smallest of them like human heads—and they did not strike anyone without killing him." The relied-upon view is that the birds were the size of swallows, and the stones were some the size of a chickpea, some smaller, and some slightly larger. Ibn Marduyah and Abu Nu'aym narrated from Abu Salih that the name of the person whom the stone would strike and the name of his father were written upon each stone; he saw this at the home of Umm Hani.