The ninety-nine names of God, al-asma al-husna, are among the most widely used devotional forms in Islam. The Quran instructs that God be called by his most beautiful names at 7:180 and 17:110 and states at 59:22-24 a sequence of them, but the Quran nowhere gives a count.
The count comes from hadith, and the core report is as strong as hadith get: it is recorded in both Sahih al-Bukhari and Sahih Muslim, which makes it muttafaq alayh, agreed upon. God has ninety-nine names, one hundred less one, and whoever ahsaha, enumerates them, or comprehends them, the verb bearing both senses, enters paradise.
The names themselves are attributes: ar-Rahman the Merciful, ar-Rahim the Compassionate, al-Malik the Sovereign, al-Quddus the Holy, and so on through qualities of power, knowledge, justice and mercy. Recitation of them is a standard devotional practice, and the misbaha, the prayer bead string, commonly carries ninety-nine beads, or thirty-three worked three times, which is also the count used in the tasbih after prayer.
The names are also the basis of a great deal of Islamic art and inscription, and of naming practice: Abd followed by one of the names, Abdullah, Abd al-Rahman, Abd al-Aziz, is among the most common naming patterns in the Muslim world, on the principle that a person may be the servant of any of the attributes.
The number is sometimes explained as indicating that the names are innumerable, ninety-nine standing for a great many rather than a closed list, and there is support for that reading in the tradition itself.