Assalamualaikum. If I ask Allah martyrdom because I want to attain firdaus ,does it comes under the ruling of sincerely asking Allah for martyrdom ? JazakAllah

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

If you mean whether the request for martyrdom to attain Al-Firdaws (highest part of paradise) is part of sincerity or contradicts it, then the answer is that it is included within sincerity and does not contradict it, because sincerity is seeking reward from Allah Alone, and you are asking for paradise from Allah with martyrdom.

Allah has urged the believers to fight for His Cause and He promised them paradise.

Allah Says (what means): {Indeed, Allah has purchased from the believers their lives and their properties [in exchange] for that they will have Paradise. They fight in the cause of Allah, so they kill and are killed. [It is] a true promise [binding] upon Him in the Torah and the Gospel and the Qur'an. And who is truer to his covenant than Allah? So rejoice in your transaction which you have contracted. And it is that which is the great attainment.} [Quran 9:111]

Allah knows best.