Chapter IV Sloka 37

ywExa<is simÏae=i¶-RSmsaTk…éte=juRn, 
}anai¶> svRkmaRi[ -SmsaTk…éte twa .

yathaidh˜Õsi samiddho'gnir
bhasmas˜tkurute'rjuna | 
jñ˜n˜gni× sarvakarm˜õi 
bhasmas˜tkurute tath˜ ( 4|37)||

As the blazing fire reduces fuel to ashes, O Arjuna, so does the fire of knowledge reduce all actions to ashes.
Commentary: Just as the seeds that are roasted cannot germinate, so also the actions that are burnt by the fire of knowledge cannot bear fruits, i.e., cannot bring man to this world again for the enjoyment of the fruits of his actions. This is reducing actions to ashes. The actions lose their potency as they are burnt by the fire of knowledge. When the knowledge of the Self dawns, all actions with their results are burnt by the fire of that knowledge just as fuel is burnt by the fire. When there is no agency-mentality (the idea "I do this"), when there is no desire for the fruits, action is no action at all. It has lost its potency. The fire of knowledge can burn all actions except the Prarabdha Karma, or the result of the past action which has brought this body into existence and which has thus already begun to bear fruits or produce effects.
According to some philosophers even the Prarabdha Karma is destroyed by the fire of knowledge. Sri Sankara says in his Aparokshanubhuti :
"In the passage ‘his actions are destroyed when the Supreme is realised’ the Veda expressly speaks of actions (Karmas) in the plural, in order to signify the destruction of even the Prarabdha."
There are three kinds of Karmas or reaction to or fructification of past actions: (1) Prarabdha, so much of the past actions as has given rise to the present birth, (2) Sanchita, the balance of the past actions that will give rise to future births-the storehouse of accumulated actions, and (3) Agami or Kriyamana, acts being done in the present life. If by the knowledge of the Self only the Sanchita and Agami were destroyed and not Prarabdha, the dual number would have been used and not the plural. (Sanskrit grammar has singular, dual and plural numbers). ( Cf. IV. 10-19)