وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ ثَوْرِ بْنِ زَيْدٍ الدِّيلِيِّ، عَنْ عَبْدِ اللَّهِ بْنِ عَبَّاسٍ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم ذَكَرَ رَمَضَانَ فَقَالَ ‏"‏ لاَ تَصُومُوا حَتَّى تَرَوُا الْهِلاَلَ وَلاَ تُفْطِرُوا حَتَّى تَرَوْهُ فَإِنْ غُمَّ عَلَيْكُمْ فَأَكْمِلُوا الْعِدَّةَ ثَلاَثِينَ ‏"‏ ‏.‏

Yahya related to me from Malik from Thawr ibn Zayd ad-Dili fromAbdullah ibn Abbas that the Messenger of Allah, may Allah bless himand grant him peace, once mentioned Ramadan and said, "Do not startthe fast or break it until you see the new moon. If the new moon isobscured from you, then complete a full thirty days." Translation Not Available

Book reference: Muwatta Imam Malik Book 18 Hadith 635
Web reference: Muwatta Imam Malik Book 18 Hadith 3