Yazid b. Mu'awiya

Hundreds of Sunni books mentioned  the fact that Yazeed did order killing of Imam Husain (AS). These are few examples : Tareekh Al-Tabari, volume 3 ; 13, V. 6; 267, V.7;11, V.11;538.

al-Imamah wal Siyaasah 1/155

Al-khasa'is Al-Khubra 2/236

al-Budayah wal-Nihayah by Ibn Katheer; 6/265

al-Kaamil by ibn Al-Atheer 6/234

Tareekh Al-Ya'qoobi 6/251

Tareekh Al-Khulafaa by Al-Soyoti 209

Morouj Al-Dgahab by Al-Mas'oodi 3/71

al-Akhbaar Al-Tiwaal by Al-Daynori 65.

Shatharaat ibn Al-Imad Al-Hanbali 1/168

Fath Al-Basri 13/70

Rasaa'il ibn Hazim 2/140

Osd Al-Ghaabah 3/243.

Wassalam.

Some Muslims pray but with out understanding the message of Prayers and don't obey the Prophet (SAWA), like the Kharijites of that time and ISIS of today.

Real Prayer which purifies us is performed with humble obedience of Allah (SWT) and the Prophet (SAWA) and Ahlul Bayt (AS).

Wassalam.

Tabari mentioned in his famous book of history Tareekh al-Tabari (V. 8, P.187) that Yazeed openly declared his infidelity and denying Islam when he saw the head of Imam Husain (AS) by saying:

 لعبت هاشم بالملك فلا.   خبرٌ جاء ولا وحيٌ  نزل

Hashim family (of the Prophet) played with rule, otherwise, nothing came from God, nor any revelation was sent.

This poem of the cursed Yazeed is narrated in many other Sunni books.

Wassalam..

We need first to define the meaning of Premature death. Because no one dies before his time. That does not mean that every death is Natural. Those who are killed have died in their own time of death. Those who died as victims of a crime of killing, died in their own time of death. We differ with some Non-Muslims who claim that there is a Premature death which means as they claim, that a person who is killed has died before his time of death. They Think that the age which is for certain age group is the maturity for death. Anyone dies before that maturity age as they claim has died Prematurely. This is their own opinion which does not come along with what we read in Quran and Authentic Hadeeths. “Wa Ma Kana Le Nafsin An Tamouta Ella Bi ‘ithnillah Kitaaban Mo’ajjala” ( 3:145)– No one dies but only by permission of Allah, according to written time” 
The way of dying can be Natural, and can be a Crime, and can be any other way. Time is written by Allah on everyone from us. Prophet Yahya (AS) was killed by a tyrant of His time instigated by a bad woman from Bani Israeel. Allah knew that such crime will happen, but the knowledge of Allah about a Crime which is to take place does not mean that Allah has permitted the killing. Allah (SWT) informed the Prophet Muhammad (peace be upon him and His Holy Progeny) that His grandson Hussain will be killed in Karbala. Also informed him that Ameerul Mo'mineen Ali (A.S.) will be killed by Ibne Muljim in Kufa. That does not mean that Allah has permitted the Crime at all. 
Wassalam.

It is a false story fabricated by Yazeed's admirers.
Yazeed did not invade Constantinople and Imam Hasan and Imam Husain had no relation with such person indulged in major sins.

Wassalam.