A section of the Mahābhārata narrates the story of Rāma. This section, called the Rāmopākhyāna, is far shorter than the Rāmāyaṇa which, as you correctly note, is a different epic altogether. The story as told in the Ramopākhyāna also differs in some details from the Rāmāyaṇa. The exact textual relationship between Valmiki's Rāmāyaṇa and the ...
The Mahabharata does not contain the Ramayana (an epic work 24000 verses long). It does, however, contain the so-called Ramopakhyana which (like the Ramayana) tells the story of Rama and Sita but (unlike the Ramayana) is only about 700 verses long. This is the "abbreviated version of the Ramayana" referred to in the Wikipedia article on the ...
Bhagavad Geeta 2:47
Source of Sandip's allusion
The passage Sandip alludes to is indeed from the Bhagavad Geeta. The exact source is Chapter 2, verse 47:
कर्मण्येवाधिकारस्ते मा फलेषु कदाचन ।
मा कर्मफलहेतुर्भूर्मा ते सङ्गोऽस्त्वकर्मणि ॥
karmaNyevaadhikaaraste ma phaleShu kadaachana
maa karmaphalaheturbhuurmaa te sa~Ngo.ostavakarmaNi