Please see David Winchester's answer at this link
https://forums.asp.net/post/3167737.aspx
I've edited his answer as following:
<asp:PasswordRecovery ID="PasswordRecovery1" runat="server">
<MailDefinition
From="noreply@gmail.com"
Subject="Your temporary password!"
IsBodyHtml="true"
Priority="High"
BodyFileName="~/Templates/PasswordRecoveryMail.htm">
</MailDefinition>
</asp:PasswordRecovery>
Content of PasswordRecoveryMail.htm file
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title></title>
</head>
<body>
<div>
Please return to the site and log in using the following information.
</div>
<p>Username: <%UserName%></p>
<p>Password: <%Password%></p>
</body>
</html>