Does lightly touching the hand of a woman -other than one's wife- invalidate ablution?

Scholars have differed on the nullification of ablution by touching women, holding three opinions:

1. Ablution is nullified by touch absolutely, even if without desire. This is the view of Ash-Shafi'i. 2. Ablution is not nullified by touch absolutely, even if with desire. This is the view of Abu Hanifa. 3. Ablution is nullified by touch if it is with desire, but not otherwise. This is the view of the Malikis and Hanbalis. The Malikis stipulate three conditions for nullification by touch: that the toucher be an adult, that the one touched be someone normally desired, and that the toucher intends pleasure or finds it.

As for the brother's wife, she is a stranger to him, and it is not permissible for him to be in seclusion with her. He must avoid touching her. However, sitting with her in the same room is permissible if she adheres to the prescribed hijab and he lowers his gaze.