The Quran

۞ وَاذكُر أَخا عادٍ إِذ أَنذَرَ قَومَهُ بِالأَحقافِ وَقَد خَلَتِ النُّذُرُ مِن بَينِ يَدَيهِ وَمِن خَلفِهِ أَلّا تَعبُدوا إِلَّا اللَّهَ إِنّي أَخافُ عَلَيكُم عَذابَ يَومٍ عَظيمٍ

(Saheeh International)

And mention, [O Muḥammad], the brother of ‘Aad,¹ when he warned his people in [the region of] al-Aḥqāf – and warners had already passed on before him and after him – [saying], "Do not worship except Allāh. Indeed, I fear for you the punishment of a terrible day."²

i.e., the prophet Hūd.
Upon the earth. It could also refer to "a tremendous Day," i.e., that of resurrection.