In Xamarin Forms 3.2.0 you can set the custom Navigation Icon & Navigation Text.
<ContentPage>
<NavigationPage.TitleView >
<StackLayout HorizontalOptions="Start" Orientation="Horizontal">
<Image HeightRequest="50" WidthRequest="50" Source="Icon"></Image>
<Label VerticalOptions="Center" Text="Pragnesh Mistry" TextColor="White" />
</StackLayout>
</NavigationPage.TitleView>
</ContentPage>
<ContentPage>
<NavigationPage.TitleView >
<StackLayout HorizontalOptions="Start" Orientation="Horizontal">
<Image HeightRequest="50" WidthRequest="50" Source="Icon"></Image>
<Label VerticalOptions="Center" Text="Pragnesh Mistry" TextColor="White" />
</StackLayout>
</NavigationPage.TitleView>
</ContentPage>