The Rules of Forgetfulness (Sahw) in Prayer
Man Lā Yaḥḍuruh al-Faqīh|Volume 1|Book 1|Chapter 50
وَقَالَ أَمِيرُ اَلْمُؤْمِنِينَ عَلَيْهِ اَلسَّلاَمُ: «سَجْدَتَا اَلسَّهْوِ بَعْدَ اَلتَّسْلِيمِ وَ قَبْلَ اَلْكَلاَمِ.
The Commander of the Faithful Imam Ali ibn Abi Talib عليه السلام said: "The two prostrations of forgetfulness (Sajdah al-Sahw) are after the Tasleem (salutation) and before speaking."
- Ṣaḥīḥ al-Faqīh