Congregational Prayer and Its Virtue
Man Lā Yaḥḍuruh al-Faqīh|Volume 1|Book 1|Chapter 57
وَ قَدْ رُوِيَ: «أَنَّهُ إِنْ كَانَ فِي صَلاَةِ اَلظُّهْرِ جَعَلَ اَلْأَوَّلَتَيْنِ اَلظُّهْرَ وَ اَلْأَخِيرَتَيْنِ اَلْعَصْرَ.
It has been narrated: "If it is during the Dhuhr prayer, he should make the first two rak'ahs for Dhuhr and the last two rak'ahs for Asr."
- Ṣaḥīḥ al-Faqīh