What is the source for "1000 raka'at during Shahri Ramadan"?

Bismillah. Alhamdulillahi rabbil-'alamin. Was-Salatu was-Salam 'ala Ashraful Anbiya Sayyidina Muhammad wa 'ala 'Alihi Muhammad. ---------- **Where is it written that one is highly recommended to pray 1000 raka'as during Shahri Ramadan?** I got it from this video and I couldn't find the source (Sunni or Shia). **I'd like also to know how it should be prayed - distribution of these 1000 raka'as across the Shahri Ramadan.**