عَنِ ابْنِ عُمَرَ رَضِيَ اللَّهُ عَنْهُ عَنِ النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَآلِهِ وَسَلَّمَ قَالَ: ((مَا مِنْ أَيَّامٍ أَعْظَمُ عِنْدَ اللَّهِ وَلَا أَحَبُّ إِلَيْهِ مِنَ الْعَمَلِ فِيهَا مِنْ هَٰذِهِ الْأَيَّامِ الْعَشْرِ، فَأَكْثِرُوا فِيهَا مِنَ التَّهْلِيلِ وَالتَّكْبِيرِ وَالتَّحْمِيدِ))
It is narrated from Sayyiduna Abdullah bin Umar, may Allah be pleased with him, that the Noble Prophet, peace and blessings be upon him, said: There are no days which are greater in the sight of Allah and in which righteous deeds are more beloved to Him than these ten days, so recite a great deal of Tahleel, Takbeer, and Tahmeed during them.