Is ablution (wudu') required upon seeing the shadow of a dog or touching its body, and is ablution invalidated by touching any part of a dog, or only its saliva, or is purifying the hand that touched the dog's saliva sufficient?

All praise is due to Allah, and may peace and blessings be upon the Messenger of Allah, his family, and his companions. To proceed:

Seeing the shadow of a dog does not invalidate ablution (wudu'), and the statement attributed to Imam Ahmad regarding this is false. Similarly, touching a dog or its saliva does not invalidate ablution. However, anything touched by a dog's saliva must be washed seven times, one of them with earth. In the case of touching a dog while it is wet, the Malikis and Hanafis do not necessitate washing because they consider the dog to be ritually pure. In contrast, the Shafi'is and Hanbalis necessitate washing the hand seven times, one of them with earth, and this is more cautious.