Caution: Translations of Quran and Ḥadīth may lead to possible misapplications and misinterpretations. This site is intended for students of sacred knowledge that are proficient in comprehending classical Arabic and have a strong foundation in Islamic sciences. Also note that religious injunctions rely on several aspects beyond what one may glean through reading individual aḥādīth.
ahmad:3474ʿAbd al-Razzāq And Ibn Bakr > Ibn Jurayj > ʿAmr b. Dīnār > Muḥammad b. Jubayr

[Machine] "to start fasting in Ramadan if the moon of Ramadan is not sighted and to say that the Prophet ﷺ said: 'if you do not see the moon, then complete thirty days.'"  

أحمد:٣٤٧٤حَدَّثَنَا عَبْدُ الرَّزَّاقِ وَابْنُ بَكْرٍ قَالَا أَخْبَرَنَا ابْنُ جُرَيْجٍ أَخْبَرَنِي عَمْرُو بْنُ دِينَارٍ أَنَّهُ سَمِعَ مُحَمَّدَ بْنَ جُبَيْرٍ يَقُولُ كَانَ ابْنُ عَبَّاسٍ يُنْكِرُ

أَنْ يُتَقَدَّمَ فِي صِيَامِ رَمَضَانَ إِذَا لَمْ يُرَ هِلَالُ شَهْرِ رَمَضَانَ وَيَقُولُ قَالَ النَّبِيُّ ﷺ إِذَا لَمْ تَرَوْا الْهِلَالَ فَاسْتَكْمِلُوا ثَلَاثِينَ لَيْلَةً