Once Ali was sleeping on the ground and was covered with dust. Muhammad happened to pass that way and said to Ali, "up Abu Turab (father of dust)." After that, this became his nickname. Once Abu Hurairah was playing with a cat when Muhammad came along and said, "Abu Hurairah (father of cats)." This nickname was so dear to him that it became his real name, so that very few people know his own name. Ibn Umar was asked whether the Prophet's companions laughed and joked. He replied that they did, though faith weighed heavier than a mountain in their hearts. Bilal ibn Sa'd said that he had seen them running between the baths and laughing to one another but when night came, they would be like monks. Jarir ibn Somura said that the Prophet always welcomed him from the time he became a Muslim and that he never saw him without a smile.
... Source and for more ---http://www.pbuh.us/prophetMuhammad.php?f=Ch_Humour
... Source and for more ---http://www.pbuh.us/prophetMuhammad.php?f=Ch_Humour