Source: Player's Guide to Faerûn
You have been initiated into the greatest secrets of Mystra's church.
Prerequisite: Cleric level 3rd, patron deity Mystra.
Benefit: You can attempt to cast spells even within a dead magic zone or an antimagic field. In a dead magic zone, you must make a successful caster level check against a DC equal to 20 + the level of the spell you are trying to cast. In an antimagic field, you must make a successful caster level check against a DC equal to 11 + the caster level of the antimagic field. If this check is successful, your spell functions normally.
In addition, you may add the following spells to your cleric spell list.