nEvidence for this is so far entirely textual
nBalâdurî
(9th c,) et al-Tabarî mention
the Sayâbiga
[=Sumatrans] in the Gulf prior to Islam and
they were apparently enrolled as mercenaries,
forming a garrison at Bahrein in the
reign of Calif Abû Bakr (632-634) as well as
becoming guardians of the treasury at Basra
and taking part in naval expeditions against
India in AD 775.