Hazrat Sulaimaan bin Shaazakooni (rahimahullah) narrates the following:

I once witnessed an incident that highlights the Taqwa and caution of Imaam Ahmed (rahimahullah). I was present in Makkah Mukarramah when he left a bucket with a grain seller as collateral so that he could purchase some grain from him (on credit) to sustain himself.

After some time, Imaam Ahmed (rahimahullah) returned to the grain seller and paid him for the grain, securing the release of his collateral. The grain seller presented two buckets to Imaam Ahmed (rahimahullah) and said, “Look at these buckets and see which belongs to you.” Imaam Ahmed (rahimahullah) replied, “I cannot identify which of the buckets belongs to me. Hence, I absolve you of my bucket as well as the money that I paid you for the grain (i.e. you may keep the bucket and the money for the grain).” Saying this, Imaam Ahmed (rahimahullah) refused to take any of the buckets.

The grain seller thereafter remarked, “By Allah! I knew which bucket belonged to him, but I merely wished to test his Taqwa!”

(Siyar A’laam min Nubalaa 9/451)