Only Allah is Ahad

The famed linguist, Muhammad al-Azhari (d. 370 A.H.), said in his Tahdheeb al-Lugha:

وأمّا اسْم الله جلّ ثَنَاؤُهُ أَحَدٌ فَإِنَّهُ لَا يُوصف شَيْء بالأحَدِيَّة غيرُه…لأنّ أحَدًا صفةٌ من صِفَات الله الَّتِي اسْتَأْثر بهَا، فَلَا يَشْركُه فِيهَا شيءٌ، وَلَيْسَ كَقَوْلِك: الله واحدٌ، وَهَذَا شَيْء واحدٌ، لِأَنَّهُ لَا يُقَال شَيْء أحَدٌ…والواحِدُ فِي صفة الله مَعْنَاهُ أَنه لَا ثَانِي لَهُ، وَيجوز أَن يُنْعَتَ الشَّيْء بأَنه وَاحِدٌ فأمَّا أَحَدٌ فَلَا يوصَفُ بِهِ غيرُ الله لِخُلوصِ هَذَا الاسمِ الشريف لَهُ جلّ ثَنَاؤُه.

And as for Allah’s name – may He be praised – Ahad, then nothing can be ascribed with this but Him…because Ahadan is an attribute from the attributes of Allah exclusively appropriated for Him. Thus, no one shares [in this attribute] with Him. It is not like your saying: Allah is one (waahid), and this thing is one (waahid) because it is not said of anything that it is Ahad… Waahid as an attribute for Allah means there is no second to Him. Other things can be ascribed as one (waahid). As for Ahad, no one is ascribed with this but Allah alone. This honorable name is exclusively His; may He be praised.