Book 65: Prophetic Commentary on the Qur'an (Tafseer of the Prophet (pbuh))
Chapter 26
"So whoever of you sights (the crescent on the first night of) the month (of Ramadan, i.e., is present at his home), he must observe Saum (fast) that month... (V.2:185)
باب {فَمَنْ شَهِدَ مِنْكُمُ الشَّهْرَ فَلْيَصُمْهُ}