Sahih al-Bukhari 1906
Book 30: Fasting · Hadith 16
Hadith text
حَدَّثَنَا عَبْدُ اللَّهِ بْنُ مَسْلَمَةَ، عَنْ مَالِكٍ، عَنْ نَافِعٍ، عَنْ عَبْدِ اللَّهِ بْنِ عُمَرَ ـ رضى الله عنهما ـ أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم ذَكَرَ رَمَضَانَ فَقَالَ " لاَ تَصُومُوا حَتَّى تَرَوُا الْهِلاَلَ، وَلاَ تُفْطِرُوا حَتَّى تَرَوْهُ، فَإِنْ غُمَّ عَلَيْكُمْ فَاقْدُرُوا لَهُ ".
Narrated `Abdullah bin `Umar:Allah's Messenger (ﷺ) mentioned Ramadan and said, "Do not fast unless you see the crescent (of Ramadan), and do not give up fasting till you see the crescent (of Shawwal), but if the sky is overcast (if you cannot see it), then act on estimation (i.e. count Sha'ban as 30 days)
Abdullah bin Umar (رضی اللہ عنہما) bataate hain: Allah ke Rasool ne Ramadan ka zikar kiya aur kaha: "Roza mat rakho jab tak tum naya chaand (Ramadan ka) na dekho, aur roza chona mat jab tak tum naya chaand (Shawwal ka) na dekho, magar agar aasman badalon se dhaka ho (agar tum ise dekh na sako), to andaza lagao (yaani Sha'ban ko 30 din maano)."
Sahih al-Bukhari 1906 · Book 30, Hadith 16