All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
Having a dog for any reason other than the three reasons mentioned in the following Hadeeth is prohibited in the Sharee’ah. Abu Hurayrah narrated that the Prophet said: “Whoever keeps a dog, one Qiraat of the reward of his good deeds is deducted daily unless the dog is used for guarding a farm, cattle, or for hunting.” [Muslim]
The same narration is reported by Al-Bukhaari and Muslim from Abu Zubayr .
It is proved that the Prophet, the Prophet said: "Angels do not get into a house where there is a picture or a dog."
As regards touching a dog, the preponderant opinion is that its saliva is impure as in a Hadeeth that reads: "The purification of the utensils belonging to anyone of you, after they have been licked by a dog, lies in washing them seven times, using sand for the first time."
The correct opinion is that anything else other than saliva, urine and dung is pure.
For more benefit on legitimate reasons for keeping a dog, please refer to Fataawa 324532, 419983, 92109, 81421, 91174 and 85829.
For more benefit on the ruling of the impurity of dogs, please read to Fatwa 82644.
Allah knows best.