Once a Greek physician, who claimed to be an expert, came to him and said: O Abul Hasan! Actually I had come to treat your elder (the Prophet) who was reportedly afflicted by madness.
But since he has died, I could not attain my desire. But I heard that you are his cousin and also his son-in-law. Now I see that your whole face and body is pale (yellowish) and both your legs are so thin that I don’t think they can withstand your body weight. I do have medicine for removal of the yellow color but there is no way of fattening your legs. It is better you walk less and carry less weight so that your legs may not break.
Then he took out some medicine for his yellow color and said: It will neither harm nor trouble you. But you will have to refrain from eating meat for forty days. The yellow color will go away. The Imam (a.s.) replied: Well, you have prescribed a medicine for removing this yellowness. Now also tell me whether you have any medicine which can increase the yellowness and which may harm me more?
That man said: Here (pointing towards another medicine) is a thing which if taken by a yellow man, can at once kill him and if he is not yellowish he may become yellow and then die. The Imam (a.s.) demanded it from that man, who gave it, telling that even a tiny particle of it can kill a man. The Imam (a.s.) at once put the whole quantity of it in his mouth and gulped it down. It made him perspire.
That fellow began to tremble fearing that he would be caught for killing the son of Abu Talib (a.s.); that no one would believe that Ali (a.s.) had killed himself. Observing his fear, the Imam smiled and said: O servant of Allah! I am now healthier than before. Your deadly medicine did not harm me at all. Now, just close your eyes. That fellow closed his eyes. Then Ali (a.s.) said: Now open your eyes and see. What he saw was that the Imam’s face had become bright and reddish. That fellow again trembled.
Smiling, the Imam asked: Where has the paleness gone? That man replied: By Allah! I feel that you are not what you were. Formerly your face, which was yellowish, is now like a red rose. The Imam said: This poison, which was deadly in your opinion, has removed my paleness. Then disclosing his legs, the Imam said: You imagine that due to weakness in my legs, I must decrease walking and refrain from taking up heavy things to protect my legs from breaking! But, now I will show that the treatment of Allah is different from yours.
Saying this, Ali (a.s.) hit the pillar on which that two-storied building had stood and which had two halls also above and, shaking that pillar, uprooted the whole structure. Seeing this, the Greek man fainted. The Imam (a.s.) got some water sprinkled on that fellow’s face and when he came to senses he spoke up: By God! I have never seen such a thing before. The Imam (a.s.) said: O Greek! You have seen the strength of these thin legs.
Where has gone your medicine now?! That fellow asked: Was the knowledge of Muhammad (S) also this much grand? The Imam (a.s.) said: My knowledge is from his knowledge and my strength is also from his strength.