From Aboo Umaamah Iyaas ibn Tha'labah who said:
The Companions of Allaah's Messenger (salallaahu 'alaihi wa'sallam) mentioned this world one day in his presence, so Allaah's Messenger (salallaahu 'alaihi wa'sallam) said: Will you not listen, will you not listen! Wearing old clothes is part if eemaan, wearing old clothes is part of eemaan!
Zuhd (abstemiousness) is to have little regard for this world, to manifest ones poverty and need before Allaah, to treat the servants of Allaah kindly and gently, to avoid spending lavishly upon clothing, food and drink, and to avoid fame.
Zuhd is not the rejection of the favours of Allaah, the One free and far removed from all defects, bestows upon some of His servants, rather it is as Shaykhul-Islaam Ibn Taymiyyah, rahimahullaah, said: Keep away from that which does not bring benefit, either because it contains no benefit at all, or because something other than it is more beneficial, so that by doing the first he would be missing greater benefit, or because it will produce something whose harm will grow to outweigh its benefit. But as regards things which are purely beneficial or predominantly, then avoidance of them is stupidity. Therefore there is to be no abstemiousness with regard to: