HttpRequest req= new HttpRequest();
    req.setMethod('POST');
    String username = 'ABC';
    String password = 'Sales123';
    Blob headerValue = Blob.valueOf(username + ':' + password);
    String authorizationHeader = 'BASIC ' + EncodingUtil.base64Encode(headerValue);
    req.setHeader('Authorization', authorizationHeader);
    Http http = new Http();
    String url = 'http://XYZ';
    req.setEndpoint(url );
    HttpResponse res = http.send(req);
    return res.getBody();

HttpRequest req= new HttpRequest();
req.setMethod('GET');
String username = 'ABC';
String password = 'Sales123';
Blob headerValue = Blob.valueOf(username + ':' + password);
String authorizationHeader = 'Basic  ' + EncodingUtil.base64Encode(headerValue);
req.setHeader('Authorization', authorizationHeader);
Http http = new Http();
String url = 'http://XYZ';
req.setEndpoint(url );
HttpResponse res = http.send(req);
return res.getBody();

Try this.

    Http httpProtocol = new Http();
    HttpRequest request= new HttpRequest();
    String url = 'http://XXXXXX';
    request.setEndpoint(url);
    request.setMethod('POST');
    request.setHeader('Authorization', getBasicAuthHeader('ABC','Sales123'));
    HttpResponse response = httpProtocol.send(request);

 public static String getBasicAuthHeader(String username, String password){
      String authHeader = '';
      authHeader = (username != null && password != null) ? 'Basic ' + EncodingUtil.base64Encode(Blob.valueOf(username + ':' + password)) : '';
      System.debug('Using Basic Authentication Header: ' + authHeader);
      return authHeader;
}

String jsonOrders ='{JSON FORMAT BODY OF THE DATA}}';
    Http http = new Http();
    HttpRequest request2 = new HttpRequest();
    request2.setEndpoint('XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX');
    request2.setMethod('POST');
    request2.setHeader('Content-Type', 'application/json; charset=utf-8');
    request2.setHeader('scope', 'XXXXXXXXXXX');
    request2.setHeader('Accept', '*/*');
    request2.setBody(jsonOrders);

    String username = 'XXXXXXXXXXX';
    String password = 'XXXXXXXXXXXXXX';
    Blob headerValue = Blob.valueOf(username + ':' + password);
    String authorizationHeader = 'Basic ' +
    EncodingUtil.base64Encode(headerValue);
    request2.setHeader('Authorization', authorizationHeader);
    //HttpResponse response = http.send(request2);
   // system.debug('The Response Body: '+response.getBody());

    HttpResponse response2 = http.send(request2);

    // Parse the JSON response
    if (response2.getStatusCode() != 201) {
        System.debug('The status code returned was not expected: ' +
            response2.getStatusCode() + ' ' + response2.getStatus());
    } else {
        System.debug(response2.getBody());
    }
    return response2;
}