Pliny, Epistle 2.20.1-6:
Piso's widow Verania was lying seriously ill -- I mean the Piso Galba adopted. Along comes Regulus. What impudence -- to intrude on her sickness when he had been her husband's deadly enemy and she hated the sight of him! The visit alone is bad enough, but he sits down by her bed and asks her the day and hour of her birth; after which he puts on a grave look and a fixed stare, moves his lips, works his fingers, and does sums. Then silence. After keeping the poor woman in suspense for a long time, he speaks: "You are going through a danger period, out of which you will pass. However, to rid you of any doubts, I will consult a soothsayer with whom I have often had dealings." Without delay he then performs a sacrifice and declares that the entrails accord with the planetary signs. Feeling her life in danger, Verania is ready to believe him; she asks for a codicil to be added to her will and puts Regulus down for a legacy. Subsequently she grows worse and dies, calling aloud on the wickedness and treachery, the worse than perjury of the man who swore her a false oath on the life of his son. This is the kind of scandalous thing Regulus is always doing, calling down the wrath of the gods (which he always manages to escape himself) on to the head of his unfortunate boy. (Loeb trans.)
Note: In Epistle 2.20.7-11, Pliny gives two more anecdotes about Regulusís legacy-hunting.