(Al-Ahqaaf) 46 : 21
وَاذْكُرْ أَخَا عَادٍ إِذْ أَنْذَرَ قَوْمَهُ بِالْأَحْقَافِ وَقَدْ خَلَتِ النُّذُرُ مِنْ بَيْنِ يَدَيْهِ وَمِنْ خَلْفِهِ أَلَّا تَعْبُدُوا إِلَّا اللَّهَ إِنِّي أَخَافُ عَلَيْكُمْ عَذَابَ يَوْمٍ عَظِيمٍ
And you make remember the brother of Aad, when he warned his people at Ahqaaf, while warners had passed before him as well as after him: You should not serve except Allah; indeed, I fear upon you a great punishment of the Day.
The Arabic word Haqaf means 'Sand hill'. Ahqaaf is the plural form of Haqaf, meaning sand hills. Ahqaaf is a desert region in the southern part of Saudi Arabia. Aad people were residing there. Prophet Hood is mentioned as the brother of Aad since he was born and lived there. See explanation 9: 31; 11: 3–4; and 21: 24–25.