Source

File: wp-admin/includes/upgrade.php

function wp_new_blog_notification( $blog_title, $blog_url, $user_id, $password ) {
		$user      = new WP_User( $user_id );
		$email     = $user->user_email;
		$name      = $user->user_login;
		$login_url = wp_login_url();

		$message = sprintf(
			/* translators: New site notification email. 1: New site URL, 2: User login, 3: User password or password reset link, 4: Login URL. */
			__(
				'Your new WordPress site has been successfully set up at:

%1$s

You can log in to the administrator account with the following information:

Username: %2$s
Password: %3$s
Log in here: %4$s

We hope you enjoy your new site. Thanks!

--The WordPress Team
https://wordpress.org/
'
			),
			$blog_url,
			$name,
			$password,
			$login_url
		);

		wp_mail( $email, __( 'New WordPress Site' ), $message );
	}