كتاب الصيام
Read the English translation first, with the original Arabic directly underneath.
It was narrated from Ribii bin Hirash, from Hudhaifah bin Al-Yaman, that the Messenger of Allah said:
"Do not anticipate the month until you see the crescent before it, or you complete the number of days. Then fast until you see the new moon, or you complete the number of days."
لاَ تَقَدَّمُوا الشَّهْرَ حَتَّى تَرَوُا الْهِلاَلَ قَبْلَهُ أَوْ تُكْمِلُوا الْعِدَّةَ ثُمَّ صُومُوا حَتَّى تَرَوُا الْهِلاَلَ أَوْ تُكْمِلُوا الْعِدَّةَ قَبْلَهُ