Disable resize of Multiline TextBox and size should grow when typing using JavaScript in ASP.Net

I want to make textbox expand while typing also to remove the drag expansion inside the textbox to avoid users dragging and expaning the textbox let the textbox expand while typing.

<%--Modal 2 Start--%>
<div class="modal fade" id="myModal1" tabindex="-1" role="dialog" aria-labelledby="myModalLabel"
    aria-hidden="true">
    <div class="modal-dialog">
        <div class="modal-content">
            <div class="modal-header">
                <button type="button" class="close" data-dismiss="modal" aria-label="Close">
                    <span aria-hidden="true">&times;</span></button><h4 class="modal-title" id="H1">
                        Details</h4>
            </div>
            <div class="modal-header">
                <asp:TextBox ID="TextBox1" runat="server" CssClass=" form-control" placeholder="Comment"></asp:TextBox></div>
            <div id="modal1body" class="modal-body">
                <div class="tblCustomer">
                    <div>
                        <div class="pull-left " style="margin-top: 2px">
                            <span><span class="name" style="font-family: Arial, Helvetica, sans-serif; font-weight: bold">
                                <%# Eval("fName") %></span>
                                <asp:Image ID="Image1" runat="server" ImageUrl='<%# String.Format("PROFILEPHOTOS/{0}",Eval("FImageName").ToString()) %>'
                                    class="image media-object img-rounded animated fadeInDown" Style="width: 45px;
                                    height: 45px;" />
                            </span><b /><span class="username">
                                <%# Eval("UserName") %></span><br />
                            <span class="postdate" style="font-family: Arial, Helvetica, sans-serif; font-weight: normal;
                                color: #C0C0C0">
                                <%# Eval("PostDate")%></span><br />
                        </div>
                        <div class="clearfix">
                        </div>
                        <div class="" style="margin-bottom: 4px">
                        </div>
                        <span class="content" style="font-family: Arial, Helvetica, sans-serif; font-weight: normal">
                            <%# Eval("Content") %></span>
                        <div class="clearfix">
                        </div>
                        <span>
                            <asp:Image ID="Image2" runat="server" ImageUrl='<%# String.Format("UserImage/{0}",Eval("ImageName").ToString()) %>'
                                class="image2 media-object img-rounded animated fadeInDown" Style="width: 30%;
                                height: 30%;" />
                        </span>
                    </div>
                </div>
            </div>
            <div class="modal-footer">
                <span>
                    <asp:LinkButton ID="LinkButton9" runat="server" CssClass="btn btn-primary btn-lg">
                        <asp:Label ID="Label26" runat="server" Text="Submit"></asp:Label>
                    </asp:LinkButton></span></div>
        </div>