# RetrievalQAWithSourcesChain

> **Class** in `langchain_classic`

📖 [View in docs](https://reference.langchain.com/python/langchain-classic/chains/qa_with_sources/retrieval/RetrievalQAWithSourcesChain)

Question-answering with sources over an index.

## Signature

```python
RetrievalQAWithSourcesChain()
```

## Extends

- `BaseQAWithSourcesChain`

## Properties

- `retriever`
- `reduce_k_below_max_tokens`
- `max_tokens_limit`

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[View source on GitHub](https://github.com/langchain-ai/langchain/blob/9f232caa7a8fe1ca042a401942d5d90d54ceb1a6/libs/langchain/langchain_classic/chains/qa_with_sources/retrieval.py#L17)