Please see the English translation of the Anapanasati Sutta (Majjhima Nikaya 118 or MN 118) on the Buddhist mindfulness of breathing technique. The transliterated Pali version can be found here.
Please see the English translation of the Satipatthana Sutta (Majjhima Nikaya 10 or MN 10) on the four foundations of mindfulness technique. The transliterated Pali version can be found here.
These two texts come from the Sutta Pitaka, the volume of the Pali Canon that contains the Buddha's discourses (suttas). According to tradition, these discourses were delivered by the Buddha, during the Buddha's lifetime (c. 563/480 – c. 483/400 BCE).
These texts, translated to English by Thanissaro Bhikkhu, are originally in the Pali language, which is a partially Sanskritized variant of Prakrit. The Buddha spoke either Magadhi Prakrit or another dialect of Prakrit. Prakrit is closely related to Sanskrit.
If you want to read a modern guide and explanation on the techniques mentioned in MN 118 and MN 10, please see Yuttadhammo Bhikkhu's book "How to Meditate". If you're actually interested to learn Buddhist meditation, this is a great place to start.
Another newer text that you may read is the Visuddhimagga or Path of Purification, a text written in the 5th century CE in Sri Lanka by the monk Buddhaghosa. You can find a PDF version here.