وَالسّابِحاتِ سَبحًا
By those who swim smoothly.
EXEGESIS
Sabḥ is accelerated motion. Sabaḥa, the root of the word sabḥ, can also mean to float or swim.
From a strictly linguistic angle, verse 3 can refer to any one of: 1. The angels that come hastily from the heavens with a command from God. 2. The stars, in reference to this verse: and each swims in an orbit (36:40). 3. The horses of soldiers as they charge forward. 4. The ships that travel over water. 5. The clouds. 6. The sea creatures.
[1] Mizan, 20/179.
[2] Lisan, 2/470.
[3] Tibyan, 10/252, narrated from Mujāhid.
[4] Tabrisi, 10/652, narrated from Qatādah and Jubbāʾī.
[5] Tabrisi, 10/652, narrated from Abū Muslim.
[6] Tabrisi, 10/652, narrated from ʿAṭāʾ.
[7] Mizan, 20/180.
[8] Mizan, 20/180.