mastodon/app/javascript/images/icon_reply.svg

<svg fill="#FFFFFF" height="24" viewBox="0 0 24 24" width="24" xmlns="http://www.w3.org/2000/svg">
    <path d="M10 9V5l-7 7 7 7v-4.1c5 0 8.5 1.6 11 5.1-1-5-4-10-11-11z"/>
    <path d="M0 0h24v24H0z" fill="none"/>
</svg>