What is the ruling on erasing the word Allaah from a chalk/whiteboard?
It iss permissible since the Prophet sallahu alayhi wa salam erased the name of Allah before as found in the Hudaibiyah Treaty:
“… The Prophet (sallallahu alaihe wa-sallam) agreed for that and said: ‘Let it be (as he says).’ Then he (sallallahu alaihe wa-sallam) dictated, ‘this is a peace treaty, which Muhammad (sallallahu alaihe wa-sallam), the Messenger of Allah has agreed with Suhail Ibn Amr.’
Suhail again objected saying, ‘Had we witnessed you as the Messenger of Allah, we would not have turned you away from the House of Allah, nor fought with you. You should write Muhammad Ibn Abdullah (Muhammad (sallallahu alaihe wa-sallam), the son of Abdullah).’
“I am Allah’s Messenger, even if you disbelieve in me,” replied the Prophet and asked Ali (radiyallahu anhu) to rub out what he had written.
‘By Allah, I cannot do it.’ replied Ali (radiyallahu anhu). The Prophet (sallallahu alaihe wa-sallam) in the larger interest of Islam, gave no importance to trivial details, he erased the words himself and dictated, “Muhammad (sallallahu alaihe wa-sallam), the son of Abdullah.”
Imam Bukharee (rahimahullah) recorded in his Saheeh in ‘The Book of Conditions,’ the terms of the peace treaty.
An excerpt from the translation of the hadeeth.
AbdulFattaah bin Uthman