Are the 16 stages of Insight mentioned by the Buddha in the early Pali texts or are they a later addition to the Dharma? I am reading Practical Insight Meditation: Basic and progressive stages by Mahasi Sayadaw. In the book he elaborates on the 16 stages of insight meditation as a kind of road map of what to expect. I was wondering if these stages are part of the Theravada tradition or an integral part of the Dharma canon.
The Seven Stages of Purification are summarised in the Visuddhimagga (The Path of Purification), a 5th century Theravada text (about 800 years after the Buddha lived).


  the seven visuddhis come from the Ratha-vinita Sutta (MN 24), and the sixteen stages of knowledge are found in the Patisambhidamagga. –  yuttadhammo
  
  This comparison between practice and "seven relay chariots" points at the goal. Each purity is needed to attain the next. They are often referred to as the "Seven Stages of Purification" (satta-visuddhi):[3]


Purification of Conduct (sīla-visuddhi)
Purification of Mind (citta-visuddhi)
Purification of View (ditthi-visuddhi)
Purification by Overcoming Doubt (kankha-vitarana-visuddhi)
Purification by Knowledge and Vision of What Is Path and Not Path (maggamagga-ñanadassana-visuddhi)
Purification by Knowledge and Vision of the Course of Practice (patipada-ñanadassana-visuddhi)
    Knowledge of contemplation of rise and fall (udayabbayanupassana-nana)
    Knowledge of contemplation of dissolution (bhanganupassana-nana)
    Knowledge of appearance as terror (bhayatupatthana-nana)
    Knowledge of contemplation of danger (adinavanupassana-nana)
    Knowledge of contemplation of dispassion (nibbidanupassana-nana)
    Knowledge of desire for deliverance (muncitukamyata-nana)
    Knowledge of contemplation of reflection (patisankhanupassana-nana)
    Knowledge of equanimity about formations (sankharupekka-nana)
    Conformity knowledge (anuloma-nana)
Purification by Knowledge and Vision (ñanadassana-visuddhi)
    Change of lineage
    The first path and fruit
    The second path and fruit
    The third path and fruit
    The fourth path and fruit



  The "Purification by Knowledge and Vision" is the culmination of the practice, in four stages leading to liberation and Nirvana.
  
  The emphasis in this system is on understanding the three marks of existence, dukkha, anatta, anicca. This emphasis is recognizable in the value that is given to vipassana over samatha, especially in the contemporary vipassana movement.