كتاب الحج
15  
The Book of Pilgrimage
(36)
Chapter: The virtue of the Umrah performed during Ramadan
(36)
باب فَضْلِ الْعُمْرَةِ فِي رَمَضَانَ ‏
Sahih Muslim 1255 b

Ataa reported:

I heard Ibn Abbas (Allah be pleased with him) narrating to us that Allah's Messenger (ﷺ) said to a woman of the Ansar (Ibn Abbas had mentioned her name but I have forgotten it): 'What has prevented you that you do not perform Hajj along with us? She said: We have only two camels for carrying water. One of the camels has been taken by my husband and my son for performing Hajj and one has been left for us for carrying water, whereupon he (the Holy Prophet) said: So when the month of Ramadan come, perform Umra, for'Umra in this (month) is equal to Hajj (in reward).
وَحَدَّثَنِي مُحَمَّدُ بْنُ حَاتِمِ بْنِ مَيْمُونٍ، حَدَّثَنَا يَحْيَى بْنُ سَعِيدٍ، عَنِ ابْنِ جُرَيْجٍ، قَالَ أَخْبَرَنِي عَطَاءٌ، قَالَ سَمِعْتُ ابْنَ عَبَّاسٍ، يُحَدِّثُنَا قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم لاِمْرَأَةٍ مِنَ الأَنْصَارِ سَمَّاهَا ابْنُ عَبَّاسٍ فَنَسِيتُ اسْمَهَا ‏"‏ مَا مَنَعَكِ أَنْ تَحُجِّي مَعَنَا ‏"‏ ‏.‏ قَالَتْ لَمْ يَكُنْ لَنَا إِلاَّ نَاضِحَانِ فَحَجَّ أَبُو وَلَدِهَا وَابْنُهَا عَلَى نَاضِحٍ وَتَرَكَ لَنَا نَاضِحًا نَنْضِحُ عَلَيْهِ قَالَ ‏"‏ فَإِذَا جَاءَ رَمَضَانُ فَاعْتَمِرِي فَإِنَّ عُمْرَةً فِيهِ تَعْدِلُ حَجَّةً ‏"‏ ‏.‏
Reference : Sahih Muslim 1255b
In-book reference : Book 15, Hadith 244
USC-MSA web (English) reference : Book 7, Hadith 2884
  (deprecated numbering scheme)