http://movieline.com/2012/06/20/prometheus-secrets-revealed-what-did-david-say-to-the-engineer/

Over at The Bioscopist blog, Stu Holmes was wondering the same question when he managed to track down the real-life linguistics expert who served as consultant on the film, Dr. Anil Biltoo of London's SOAS Language Centre. Biltoo not only taught Fassbender how to speak in Proto-Indo-European (PIE) language as the android David — seen studying ancient communication as the crew sleeps in the film's opening measures — he also appeared onscreen as the holographic linguistics teacher David learns from as he recites the real-life text Schleicher's Fable, a story created in 1868 in the reconstructed PIE language.

While Scott, Damon Lindelof, and Co. remain mum about Prometheus's many open-ended provocations, Biltoo revealed what it is that David whispers to the Engineer at the end of the film, setting off the being's violent rampage:

The line that David speaks to the Engineer (which is from a longer sequence that didn’t make the final edit) is as follows:

/ida hmanəm aɪ kja namṛtuh zdɛ:taha/…/ghʷɪvah-pjorn-ɪttham sas da:tṛ kredah/

A serviceable translation into English is:

‘This man is here because he does not want to die. He believes you can give him more life’.