A person mistakenly gives Salaam after 2 rak'ahs of a 4-rak'ah prayer, thinking the prayer was complete. What should be done if no incompatible act has occurred?

Sujud al-Sahw: Cause, Method, Timing, and Special Cases

• Complete the remaining rak'ahs and perform Sujud al-Sahw.
• Treat the 2 rak'ahs as permanently complete Fard.
• Start a different prayer.
• Only repeat the Salaam.