Sahih Bukhari, Chapter: Times of the Prayers

The Prophet said, "The example of Muslims, Jews and Christians is like the example of a man who employed laborers to work for him from morning till night. They worked till mid-day and they said, 'We are not in need of your reward.' SO the man employed another batch and said to them, 'Complete the rest of the day and yours will be the wages I had fixed (for the first batch). They worked Up till the time of the 'Asr prayer and said, 'Whatever we have done is for you.' He employed another batch. They worked for the rest of the day till sunset, and they received the wages of the two former batches."