Ramayana 6.181

Then Rama, while his spirit burned For battle, words like these returned: "The eastern gate be Nila's care, Opponent of Prahasta there. The southern gate, with troops arrayed Let Angad, Bali's son, invade. The gate that fronts the falling sun Shall be by brave Hanuman won; Soon through its portals shall he lead His myriads of Vanar breed. The gate that fronts the north shall be Assailed by Lakshman and by me, For I myself have sworn to kill The tyrant who delights in ill. Armed with the boon which Brahma gave, The Gods of heaven he loves to brave, And through the trembling worlds he flies, Oppressor of the just and wise. Thou, Jambavan, and thou, O King Of Vanars, all your bravest bring, And with your hosts in dense array Straight to the centre force your way. But let no Vanar in the storm Disguise him in a human form, Ye chiefs who change your shapes at will, Retain your Vanar semblance still. Thus, when we battle with the foe, Both men and Vanars will ye know, In human form will seven appear; Myself, my brother Lakshman here; Vibhishan, and the four he led From Lanka's city when he fled."