For untimed worship, the intention must identify the particular duty, and it must be made before beginning the act.
Compare:
• In paying Zakat, the intention is to fulfill Zakat, not merely to give money.
• In a Ramadan Qada fast, the intention is to fulfill that Qada fast, not merely to keep any fast.
Identifying the particular worship in the intention is called Ta'yin1. These examples explain the intention; they are not prescribed phrases to recite.
1. Ta'yin: specifying which worship or duty one intends to perform.
- Intend the Particular Duty