Sunan Ibn Majah, Volume 4, Book 25, Hadith 2994 (DarusSalam) ⓘ
It was narrated from Ibn ‘Abbas that the Messenger of Allah said: “Umrah during Ramadan is equivalent to Hajj.”
حَدَّثَنَا عَلِيُّ بْنُ مُحَمَّدٍ، حَدَّثَنَا أَبُو مُعَاوِيَةَ، عَنْ حَجَّاجٍ، عَنْ عَطَاءٍ، عَنِ ابْنِ عَبَّاسٍ، قَالَ قَالَ رَسُولُ اللَّهِ ـ صلى الله عليه وسلم ـ " عُمْرَةٌ فِي رَمَضَانَ تَعْدِلُ حِجَّةً " .
also referenced under: Hadith 2994 (Reference) & Book 25, Hadith 3108 (In-Book)