What is the meaning of Zuhd (asceticism) in Islam, and does it include sleeping on the ground without a mattress when a bed is available, and is it limited to eating bread and drinking water when other food is accessible?

Asceticism (Zuhd) in this world is not about forbidding the good things, but rather it is the heart's journey from this world to the Hereafter. Imam Ahmad defined it in three ways: abandoning the unlawful (the asceticism of the common folk), abandoning the superfluous lawful things (the asceticism of the elite), and abandoning whatever distracts one from Allah (the asceticism of the Gnostics). A servant does not deserve the name of asceticism until he abstains from wealth, appearances, leadership, people, the self, and everything other than Allah. This does not mean rejecting ownership of these things, for the prophets and companions were ascetics despite their possessions and wealth. True asceticism is for the servant to be more confident in what is with Allah than in what is in his own hand, and to desire the reward of affliction more than its absence. The ascetic is content with what Allah has given him, does not grieve over what he has missed, and does not attach his heart to anything other than his Lord. He is one whom the unlawful does not overcome, and the lawful does not distract him from gratitude. When he is blessed, he is grateful, and when he is afflicted, he is patient. He has short hopes and despairs of what is in people's hands. The true ascetic is one who accompanies Allah without creation and accompanies people without self.