Source: Dragon #325
You can prepare any of your spells as either divine or arcane.
Prerequisite: Ability to cast both divine and arcane spells.
Benefit: You can choose to prepare any of your divine spells as arcane spells or any of your arcane spells as divine spells. An alternative-sourced spell uses up a spell slot from the class that normally grants the spell. Such a spell is prepared normally. An alternative-sourced spell is cast as if your caster level were 1 level lower. For example, a 1st-level cleric/6th-level wizard casts a divine fireball as a 5th-level wizard.