For those who are interested in roots and origin of mindfulness, should take a look at original Anapanasati Sutta (https://www.accesstoinsight.org/tipitaka/mn/mn.118.than.html). Anapanasati Sutta is the main source from which all the modern literature related to mindfulness has been derived. For more detailed explanation of sutta, listen to talk on mindfulness of breathing (https://www.youtube.com/watch?v=p4NR3nn4nfM).