The clever play by William Shakespeare which has the line: "Things sweet to taste prove in digestion sour" is "Richard II". This quote is specifically given in Act I, scene 3 (line 237) by John of Gaunt while he is talking to King Richard II.

John is telling the king that sometimes a thing that tastes sweet later makes you feel sick. The king asked him to be a judge, but he would rather have been a father who argued and behaved as a father. If it had been a stranger rather than his own son, John would have been more straightforward and have gone easier on him. He wanted to avoid seeming soft. However, in the process, he appears to have mostly destroyed himself. Alas, he had expected someone to say that he was too strict in helping to banish his own son, but the king and others let John of Gaunt agree to the terrible decision.

King Richard finally tunes out John and tells him to say adios to his son. John must live with the sour taste.

More Info: