Let $R$ be complete local ring $M$ be the maximal ideal of $R$
$F$ be a formal group defined over $R$, with group law $F（X,Y）$.
According Silverman's book 'the arithmetic of elliptic curves', example 6.1.1,
If $R$ is integers in any field unramified extension of $\Bbb Q_p$,then group associated to formal group $F$,$F（M）$ has no torsion.
But there are no proof or reference. I searched a lot, but I couldn't find article regarding this problem.
How to prove this?
Reference（pdf,book） is also appreciated, thank you for your help.