A trustworthy narrator informed us that Mujahid (may Allah have mercy on him) used to say: Thunder (ra'd) is an angel, and lightning (barq) is the wings of the angel, which drive the clouds. Imam al-Shafi'i (may Allah have mercy on him) said: How closely what Mujahid (may Allah have mercy on him) said resembles the apparent meaning of the Qur'an!
Hadith Referenceالسنن الكبرى للبيهقي / كتاب صلاة الاستسقاء / 6475
Umar bin Abi Za'idah (may Allah have mercy on him) said: I heard Ikrimah (may Allah have mercy on him) when a man asked him about the words of Allah Almighty: "And the thunder glorifies with His praise" [Surah al-Ra'd: 13]. He said: It is an angel who drives the clouds, just as the camel driver drives the camels.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب صلاة الاستسقاء / 6476
Abu Muhammad al-Hashimi narrates from his father, and he from Ali (may Allah be pleased with him), that thunder (al-ra'd) is an angel, and lightning (al-barq) is a whip of iron.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب صلاة الاستسقاء / 6477
Al-Mughirah bin Muslim, the freed slave of Sayyiduna al-Hasan bin Ali (may Allah be pleased with them both), narrates from his father that Sayyiduna Ali (may Allah be pleased with him) said: Thunder is an angel.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب صلاة الاستسقاء / 6478