Shri Krishna was described as adherent to TRUTH and DHARMA by Sage Vyasa.
This issue was substantiated by the fact that Shri Krishna revived the dead Parikshit, by using the ascetic power of adherence to TRUTH and DHARMA. This was what Shri Krishna said consoling the wailing Uttara.
न ब्रवीम्युत्तरे मिथ्या सत्यमेतद्भविष्यति । एष सञ्जीवयाम्येनं पश्यतां सर्वदेहिनाम् ॥
नोक्तपूर्वं मया मिथ्या स्वैरेष्वपि कदाचन । न च युद्धे परावृत्तस्तथा सञ्जीवतामयम् ॥
यथा मे दयितो धर्मो ब्राह्मणाश्च विशेषतः । अभिमन्योः सुतो जातो मृतो जीवत्वयं तथा ॥
यथाहं नाभिजानामि विजयेन कदाचन । विरोधं तेन सत्येन मृतो जीवत्वयं शिशुः ॥
यथा सत्यं च धर्मश्च मयि नित्यं प्रतिष्ठितौ । तथा मृतः शिशुरयं जीवतामभिमन्युजः ॥
यथा कंसश्च केशी च धर्मेण निहतौ मया । तेन सत्येन बालोऽयं पुनरुज्जीवतामिह ॥
इत्युक्तो वासुदेवेन स बालो भरतर्षभ । शनैः शनैर्महाराज प्रास्पन्दत सचेतनः ॥
ततस्तस्यै ददौ प्रीतो बहुरत्नं विशेषतः ॥
तथान्ये वृष्णिशार्दूला नाम चास्याकरोत्प्रभुः । पितुस्तव महाराज सत्यसन्धो जनार्दनः ॥
परिक्षीणे कुले यस्माज्जातोऽयमभिमन्युजः । परिक्षिदिति नामास्य भवत्वित्यब्रवीत्तदा ॥
Then Krishna, said these words in the hearing of the whole universe,--'O Uttara, I never utter an untruth. My words will prove true. I shall revive this child in the presence of all creatures. Never before have I uttered an untruth even in jest. Never have I turned back from battle. (By the merit of those acts) let this child revive! As righteousness is dear to me, as Brahmanas are specially dear to me, (by the merit of that disposition of mine) let Abhimanyu's son, who is born dead, revive! Never hath a misunderstanding arisen between me and my friend Vijaya. Let this dead child revive by that truth!
As truth and righteousness are always established in me, let this dead child of Abhimanyu revive (by the merit of these)! As Kansa and Kesi have been righteously slain by me, let this child revive today by that truth!'
After these words were uttered by Vasudeva, that child, O foremost one of Bharata's race, became animate and began gradually to move, O monarch.'
Janardana and other Vrishni warriors gave presents to the child. Krishna bestowed a name on the infant 'Since this child of Abhimanyu has been born at a time when this race has become nearly extinct, let his name be Parikshit!'
This incident occurred after the war and the coronation of Yudhisthira as the emperor.
Had Shri Krishna uttered anything UNTRUTH or did anything which is not according to path of TRUTH before this revival of Parikshit, Shri Krishna could not have revived Parikshit, as the NATURE or the God, is the witness to all thoughts and actions of all human beings.
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Now, let us consider what Shri Krishna said when Duryodhana and Arjuna asked for the former’s assistance in the impending war.
In the Udyoga Parva, it was mentioned that when Duryodhana and Arjuna went to Dwaraka for seeking the assistance of Yadavas in the impending war, Shri Krishna says as follows:
ते वा युधि दुराधर्षा भवन्त्वेकस्य सैनिकाः । अयुध्यमानः सङ्ग्रामे न्यस्तशस्त्रोऽहमेकतः ॥
आभ्यामन्यतरं पार्थ यत्ते हृद्यतरं मतम् । तद्वृणीतां भवानग्रे प्रवार्यस्त्वं हि धर्मतः ॥
These soldiers, irresistible in battle, shall be sent to one of you and I alone, resolved not to fight on the field, and laying down my arms, will go to the other. You, son of Kunti (Arjuna), may first choose whichever of these two appeals to you. By law, you have the right to the first choice.
So, Shri Krishna clearly said that he would not fight and take up arms, during the impending war, between Kauravas and Pandavas.
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Finally, it was what narrated in the 3rd and 9th day of the war, in respect of Shri Krishna’s taking up weapons.
ततः सुनाभं वसुदेवपुत्रः; सूर्यप्रभं वज्रसमप्रभावम् । क्षुरान्तमुद्यम्य भुजेन चक्रं; रथादवप्लुत्य विसृज्य वाहान् ॥
सङ्कम्पयन्गां चरणैर्महात्मा; वेगेन कृष्णः प्रससार भीष्मम् । मदान्धमाजौ समुदीर्णदर्पः; सिंहो जिघांसन्निव वारणेन्द्रम् ॥
Saying this, Vasudeva's son, abandoning (the reins of) the steeds, jumped down from the car, whirling with his (right) arm his discus of beautiful nave with edge sharp as a razor, effulgent as the sun and possessed of force equal to that of a thousand bolts of heaven. And making the earth tremble under his tread, the high-souled Krishna rushed impetuously towards Bhishma.
नामृष्यत महाबाहुर्माधवः परवीरहा । उत्सृज्य रजतप्रख्यान्हयान्पार्थस्य मारिष ।
क्रुद्धो नाम महायोगी प्रचस्कन्द महारथात् ॥
अभिदुद्राव भीष्मं स भुजप्रहरणो बली । प्रतोदपाणिस्तेजस्वी सिंहवद्विनदन्मुहुः ।
दारयन्निव पद्भ्यां स जगतीं जगतीश्वरः ।क्रोधताम्रेक्षणः कृष्णो जिघांसुरमितद्युतिः ॥
Abandoning then, O sire, Partha's steeds that looked like silver, and filled with wrath, that great lord of Yoga powers jumped down from that great car. Repeatedly roaring like a lion, the mighty Krishna of great energy and immeasurable splendour, the Lord of Universe, with eyes red as copper from rage, and having his bare arms alone for his weapons, rushed towards Bhishma, whip in hand, desirous of slaying him and seeming to split the universe itself with his tread.
If we carefully study the above narrations, we can find that on the 3rd day of the war it was mentioned that Shri Krishna took up his Chakra (discus) and rushed towards Bhishma to kill him, while on the 9th day of the war it was mentioned that he rushed towards Bhishma to kill him, with only whip - to drive the chariot - in his hand.
Hence, on both the occasions, Shri Krishna was stated to have an intention to kill Bhishma, which is contradicting his word that he would not fight in the war.
This implies that Shri Krishna had deviated from the path of TRUTH. If this is true, then he would not have been able to revive the dead Parikshit stating that he never utter UNTRUTH.
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Thus, these incidents of Shri Krishna rushing towards Bhishma to kill him, with or without weapon, are interpolated versions, added some later date scholar.
