I was reading through Patisambhidamagga, KN. From page 164, it describes about 'Eighteen kinds of knowledge of imperfections' related to Anapanasati(Mahavagga->Anapanasatikatha).
Following is the except:
1)When he goes in with mindfulness after the beginning, middle and end of the in-breath, his cognizance being distracted internally, both his body and his cognizance are disquieted, perturbed and excited.
2)When he goes out with mindfulness after the beginning, middle and end of the out-breath, his cognizance being distracted internally, both his body and his cognizance are disquieted, perturbed and excited.
3)With such behavior of craving as hope for, and attachment to, in-breath both his body and his cognizance are disquieted, perturbed and excited.
4)With such behavior of craving as hope for, and attachment to, out-breath both his body and his cognizance are disquieted, perturbed and excited.
5)Owing to longing for out-breath in him when he is fatigued by [too long or too short] in-breath is body..
....
Does anybody have a reference to pali canon(not commentary) where it supports the observation of start-middle-end of breath?