Al-Kāfi

Hadith 538
fastingmenstruation
4ـ صَفْوَانُ بْنُ يَحْيَى عَنْ عَبْدِ الرَّحْمَنِ بْنِ الْحَجَّاجِ قَالَ سَأَلْتُ أَبَا الْحَسَنِ (عَلَيْهِ السَّلاَم) عَنِ الْمَرْأَةِ تَلِدُ بَعْدَ الْعَصْرِ أَ تُتِمُّ ذَلِكَ الْيَوْمَ أَمْ تُفْطِرُ قَالَ تُفْطِرُ وَتَقْضِي ذَلِكَ الْيَوْمَ.
4. From Safwan ibn Yahya has narrated from ‘Abd al-Rahman ibn al-Hajjaj who has said the following: “I once asked abu al-Hassan (a.s.), about the case of a woman who gives birth after al-‘Asr if she completes or stops fasting on that day. He (the Imam) said, ‘She must stop fasting, and complete Qada’ (compensatory fast) of that day.’”
Source: Shaykh Muḥammad b. Yaʿqūb al-Kulaynī