The spiritual retreat during the last ten days of Ramadan is known as al-sunna al-mu'akkada 'ala al-kifaya. This means that if all of the people in a certain locality omit it, every person amongst them will be blamed. However, if one of them performs it, none will be blamed on the Day of Judgement. More plainly, this is not a responsibility upon every individual in a locality. It is rather a collective responsibility, which is lifted from all the people in a locality if some of them perform it. 'Abd Allah b. 'Umar (R.A) narrates that the Prophet (pbuh) used to perform spiritual retreat for the last ten days of Ramadan.