This scene occurs at the beginning of Act III. (If you need the text of the play, eNotes has it available in a highly accessible form, with helpful annotation.)
Macbeth cleverly convinces the murderers that Banquo is their enemy and that their misfortunes are his fault. (Are you so gospell'd/
To pray for this good man and for his issue,/ Whose heavy hand hath bow'd you to the grave/And beggar'd yours for ever? Act III, Scene 1).
Macbeth insists that Banquo is his enemy, as well. As he explains to the murderers, however, he cannot kill Banquo himself, for they share friends whom Macbeth must not offend or otherwise wrong by committing the murder. (For certain friends that are both his and mine,/Whose loves I may not drop, but wail his fall/Who I myself struck down; and thence it is,/That I to your assistance do make love,/Masking the business from the common eye/For sundry weighty reasons. Act III, Scene 1)