Halliday & Matthiessen (1999: 115):
However, reported offers can always be realised in the same way as reported commands — as in the case of reported propositions, the distinction in orientation between giving and demanding is realised by the projecting clause; for example:command: she told him —> to do the laundryoffer: she offered (promised; threatened) —> to do the laundryThe category of reported proposal is thus realised generally as a perfective non-finite clause when it is reported.