We went out to perform Umra and when we encamped in the valley of Nakhla, we tried to see the new moon. Some of the people said: It was three nights old, and others (said) that it was two nights old. We then met Ibn 'Abbas and told him we had seen the new moon, but that some of the people said it was three nights old and others that it was two nights old. He asked on which night we had seen it; and when we told him we had seen it on such and such night, he said the Prophet of Allah ﷺ had said: Verily Allah deferred it till the time it is seen, so it is to be reckoned from the night you saw it.  

خَرَجْنَا لِلْعُمْرَةِ فَلَمَّا نَزَلْنَا بِبَطْنِ نَخْلَةَ قَالَ تَرَاءَيْنَا الْهِلاَلَ فَقَالَ بَعْضُ الْقَوْمِ هُوَ ابْنُ ثَلاَثٍ وَقَالَ بَعْضُ الْقَوْمِ هُوَ ابْنُ لَيْلَتَيْنِ قَالَ فَلَقِينَا ابْنَ عَبَّاسٍ فَقُلْنَا إِنَّا رَأَيْنَا الْهِلاَلَ فَقَالَ بَعْضُ الْقَوْمِ هُوَ ابْنُ ثَلاَثٍ وَقَالَ بَعْضُ الْقَوْمِ هُوَ ابْنُ لَيْلَتَيْنِ فَقَالَ أَىَّ لَيْلَةٍ رَأَيْتُمُوهُ قَالَ فَقُلْنَا لَيْلَةَ كَذَا وَكَذَا فَقَالَ إِنَّ رَسُولَ اللَّهِ ﷺ قَالَ إِنَّ اللَّهَ مَدَّهُ لِلرُّؤْيَةِ فَهُوَ لِلَيْلَةِ رَأَيْتُمُوهُ  

We saw the new moon of Ramadan as we were at Dhit-i-'Irq. We sent a man to Ibn Abbas (Allah be pleased with both of them) to ask him (whether the sighting of a small moon had something of the nature of defect in it). Upon this Ibn 'Abbas (Allah be pleased with both of them) said that the Messenger of Allah ﷺ had said: Verily Allah deferred its sight, but if (the new moon) is hidden from you, then, complete its number (thirty).  

قَالَ رَسُولُ اللَّهِ ﷺ إِنَّ اللَّهَ قَدْ أَمَدَّهُ لِرُؤْيَتِهِ فَإِنْ أُغْمِيَ عَلَيْكُمْ فَأَكْمِلُوا الْعِدَّةَ