Valmiki Ramayana Sundara Kanda Sarga 37 Shloka 24
Original Shlokaपृष्ठमारोह मे देवि मा विकाङ्क्षस्व शोभने। योगमन्विच्छ रामेण शशाङ्केनेव रोहिणी।।5.37.24।।
1 source checked for this shloka
देवि O god like lady, मम my, पृष्ठम् back, आरोह climb up, शोभने O beautiful one, मा विकाङ्क्षस्व do not be reluctant, रोहिणी Rohini, शशाङ्केनेव like joining with the Moon, रामेण with Rama, योगम् union, अन्विच्छ you may become.
"O god like lady climb up my back. Do not be reluctant. Join Rama just as Rohini unites with the Moon, O beautiful one