In ancient times, urine was a valuable commodity and many people collected it and then delivered it for a fee to manufactories that used it to bleach the material and remove stains. Due to this practice and the desire to provide additional funds to the state treasury, in 74 CE, Emperor Vespasian introduced urine tax (urinae vectigal).
His son Titus criticized the new law. Then Vespasian:
[…] held a piece of money from the first payment to his son’s nose, asking whether its odour was offensive to him. When Titus said “No,” he replied, “Yet it comes from urine.”
– Suetonius, Vespasian, 23
After Vespasian’s death, Titus withdrew the tax.
Interestingly, there are popular words: Pecunia non olet, meaning “money does not stink” – words that Vespasian was to say as a reaction to criticism of his son. We do not find any confirmation for those words in ancient sources and they have certainly become simply a phrase intended to emphasize that money can be earned on any business.