Praise be to Allaah.
Allaah has many names, all of which are indicative of His Greatness, Perfection and Majesty, may He be glorified and exalted. He has told us some of these Names in His Book and through the Sunnah of His Messenger (peace and blessings of Allaah be upon him); He also has other Names which are known only to Him, as is indicated in the hadeeth of 'Abdullah ibn Mas'ood (may Allaah be pleased with him), who said:
"The Messenger of Allaah (peace and blessings of Allaah be upon him) said: 'There is nobody who is afflicted with distress or grief and who says: "Allaahumma inni 'abduka wa ibn 'abdika wa ibn amatika, naasiyati bi yadika maadin fiyya hukmuka 'adlun fiyya qadaa'uka, as'aluka bi kulli ismin huwa laka sammayta bihi nafsaka aw 'allamtahu ahadan min khalqika aw anzaltahu fi kitaabika aw asta'tharta bihi fi 'ilmi al-ghaybi 'indaka an taj'al al-Qur'aana rabee'a qalbi wa noor sadri wa jilaa'a huzni wa dhihaaba hammi (O Allaah, I am Your slave, son of Your slave, son of Your maidservant, my forelock is in Your hand, Your command over me is ever executed and Your decree over me is just. I ask You by every name belonging to You which You have named Yourself with, or revealed in Your Book, or You taught to any of Your creation, or You have preserved in the knowledge of the Unseen with You, that You make the Qur'aan the life of my heart and the light of my breast, and a departure for my sorrow and a release for my anxiety," - but Allaah will take away his distress and grief, and replace it with ease.' He was asked, 'O Messenger of Allaah, should we not learn it?' He said, 'Of course, whoever hears it should learn it.'" (Reported by Imaam Ahmad; this is a saheeh hadeeth).
The Names of Allaah mentioned in the Qur'aan and Sunnah number over one hundred, as several scholars have agreed (see Al-Qawaa'id al-Muthlaa fi Sifaat Allaahi wa Asmaa'ihi by Shaykh Muhammad ibn Saalih ibn 'Uthaymeen).
Among these are ninety-nine names which, if one learns them and acts in accordance with them, will bring a great reward, as is indicated in the hadeeth narrated by Abu Hurayrah (may Allaah be pleased with him), in which the Messenger of Allaah (peace and blessings of Allaah be upon him) said: "Allaah has ninety-nine names, one hundred less one; whoever learns them will enter Paradise." (Reported by al-Bukhaari, al-Fath, no. 2736)
The learning referred to in the hadeeth includes the following:
Understanding their meanings.
Acting upon them: so if a person learns that Allaah is al-Ahad (the One and Only), he will not associate anything else with Him; if he learns that He is al-Razzaaq (the Provider), he will not seek provision from anyone else; if he learns that He is al-Raheem (the Most Merciful), he will not despair of His Mercy, and so on.
Calling upon Allaah by these Names, as He says (interpretation of the meaning): "And (all) the Most Beautiful Names belong to Allaah, so call on Him by them…" [al-A'raaf 7:180] - so one might say "Yaa Rahmaan arhamni (O Most Merciful, have mercy on me)," "Yaa Ghafoor ighfir li (O All-Forgiving, forgive me)," "Yaa Tawwaab, tubb 'alayya (O Accepter of Repentance, turn towards me in forgiveness)," and so on.
If you pay attention to the endings of many aayaat, you will find many of the names of Allah mentioned there. And Allaah knows best.
Sheikh Muhammed Salih Al-Munajjid