Valmiki Ramayana Sundara Kanda Sarga 51 Shloka 24

अत्यर्थम् excessive, विषसंसृष्टम् mixed with poison, भुक्तम् eaten, अन्नमिव like food, इयम् this, सासुरैः including asuras, अमरैरपि even gods, ओजसा absorb, जरयितुम् to weaken, न शक्या not possible.

"Just as food mixed with venom cannot be digested by the great fire (fire of hunger), it is not possible to keep Sita even by gods and demons. (Sita is like food mixed with poison. Ravana cannot digest her with all his power.)