Exodus 10:21-23

ASV_Strongs(i)
  21 H3068 And Jehovah H559 said H4872 unto Moses, H5186 Stretch out H3027 thy hand H8064 toward heaven, H2822 that there may be darkness H776 over the land H4714 of Egypt, H2822 even darkness H4959 which may be felt.
  22 H4872 And Moses H5186 stretched forth H3027 his hand H8064 toward heaven; H653 and there was a thick H2822 darkness H776 in all the land H4714 of Egypt H7969 three H3117 days;
  23 H7200 they saw H376 not one H251 another, H6965 neither rose H376 any H7969 one from his place for three H3117 days: H1121 but all the children H3478 of Israel H216 had light H4186 in their dwellings.