The Rules of Forgetfulness (Sahw) in Prayer
Man Lā Yaḥḍuruh al-Faqīh|Volume 1|Book 1|Chapter 50
وَ رَوَى عَامِرُ بْنُ جُذَاعَةَ عَنْهُ عَلَيْهِ اَلسَّلاَمُ أَنَّهُ قَالَ: «إِذَا سَلِمَتِ اَلرَّكْعَتَانِ اَلْأَوَّلَتَانِ سَلِمَتِ اَلصَّلاَةُ.
Amir ibn Jadh'ah narrated from Imam عليه السلام that He said: "If the first two rak'ahs are correct, the whole prayer is correct”.
- Ṣaḥīḥ al-Faqīh, p. 46