سُبْـحانَ الّذي يُسَبِّـحُ الـرَّعْدُ بِحَمْـدِهِ، وَالملائِكـةُ مِنْ خيـفَته
Subhaanal-lathee yusabbihur-ra du bihamdihi walmalaa ikatu min kheefatihi.
Glory is to Him Whom thunder and angels glorify due to fear of Him.
Reference: Whenever Abdullah bin Zubair (RA) would hear thunder, he would abandon all conversation and say this supplication. See Al-Muwatta 2/992. It was graded authentic by Al-Albani as a statement of Abdullah bin Zubayr only.