In one narration the words are: "The Prophet (peace and blessings be upon him) would place his right hand on his forehead and then recite: 'Allahumma adhhib 'annil-hamma wal-hazan'
"O Allah, remove anxiety and grief from me."
Al-Tabarani recorded it in al-Mu'jam al-Awsat, and al-Bazzar recorded something similar through various chains. Its chain contains Zayd al-Ammi, whom more than one scholar declared trustworthy while the majority declared him da'if (weak). The remaining narrators of one of al-Tabarani's two chains are thiqat (trustworthy), and there is disagreement about some of its narrators.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الأذكار / 16972