Spontaneous Spell

 
Prerequisite(s): Character Level 21+, Spellcraft 25+ ranks, ability to cast the maximum normal spell level of at least one spell-casting class.
 
Benefit: Select a spell the character can cast. The character may spontaneously convert any prepared spell of the selected spell’s level into the selected spell, just as a cleric channels energy to convert spells into cure spells.
 
Special: A character can gain this feat multiple times. Each time a character takes the feat, it applies to a different spell.
 
Source: Epic Level Handbook