Abdullah ibn-`Umar (May Allah be pleased with him) reported that Prophet Muhammad (sallallaho alaihi wa sallam) said: There are no days greater in the sight of Allah and in which righteous deeds are more beloved to Him than these ten days (of Dhul-Hijjah). So, during this time, recite a great deal of Tahlil (saying Laa ilaaha illa-Allah: there is no god but Allah), Takbeer (Allahuakkbar) and Tahmid (alhumdulillaah). (Reported by Ahmad.)