Al-Kāfi - Volume 1 > Chapter On the Coming into the Existence of the Names of Allah
Hadith #3

3ـ وَبِهَذَا الاسْنَادِ عَنْ مُحَمَّدِ بْنِ سِنَانٍ قَالَ سَأَلْتُهُ عَنِ الاسْمَ مَا هُوَ قَالَ صِفَةٌ لِمَوْصُوفٍ.

3. It is narrated through the same chain of narrators (as in the above Hadith) from Muhammad ibn Sinan who has said the following. “I asked the Imam, (perhaps abu al-Hassan al-Rida) about the name (of Allah), ‘What is it?’ The Imam replied, “It is an attribute of the attributes of (Allah).”