All perfect praise be to Allah the Lord of the Worlds. May His peace and blessings be upon our Prophet Mohammad and upon all his family and companions.
From an Islamic viewpoint, it is forbidden to obtain a false sick leave without actually being sick. The evidence on this is that Allah, Exalted may He be, Says (What means): "O ye who believe! Fear God and be with those who are true (in word and deed)." {At-Tawbah, 119}. Moreover, 'Abdullah reported Allah's Messenger (PBUH) as saying: "It is obligatory for you to tell the truth, for truth leads to virtue and virtue leads to Paradise, and the man who continues to speak the truth and endeavours to tell the truth is eventually recorded as truthful with Allah, and beware of telling of a lie for telling of a lie leads to obscenity and obscenity leads to Hell-Fire, and the person who keeps telling lies and endeavours to tell a lie is recorded as a liar with Allah." {Related by Bukhari & Muslim}.
As for the doctor who gives the employee a sick note that allows him more time off than he deserves and without actually being sick, he is a liar and a deceiver to the Muslim Ummah. This is attested to in the Hadith where the Messenger of Allah Says: "He who deceives is not of me (is not my follower)." {Related by Muslim}.
In conclusion, it isn`t permissible for an employee to get a sick leave without a lawful excuse or else he incurs sin and the same ruling applies to the doctor issuing that leave. In addition, what the latter has done reflects that the medical establishment where he works rets on lying and deception. Moreover, the wages that the employee is paid during that false sick leave are unlawful. We (Iftaa` Dept.) advise all to fear Allah and be with the truthful. And Allah the Almighty Knows Best.