The Hervarar Saga ok Heiðreks on Loki
Stories And Ballads > Part I > The TháTtr Of SöRli
attestation: Loki son of Farbauti was cunning but was hated by all because of his spitefulness
"There was a man called Farbau"
attestation: Loki turned into a flea to steal Freyja's necklace while she slept
"Loki thereupon turned himself into a flea and settled on Freyja's cheek and stung her, till she awoke and turned over and went to sleep again."
attestation: Loki drew the necklace from Freyja gently and carried it to Othin
"he laid aside his flea-form, drew the necklace from her gently, opened the door and departed, carrying the necklace to Othin."
attestation: Loki entered Freyja's locked bower by finding the clasp underneath her as she slept
"he went in and up to Freyja's bed and found that she was wearing the necklace and that the clasp was underneath her."