I have heared and also when I was accepting Islam they told me that now "your all past sins are forgiven can anyone tell me any verse from the sunnah or Quran .
In the name of God, the Most Merciful, the Most Kind.
I assume that you have converted to Islam? What you have heard from others telling you that Islam wipes all sins from your past no matter how big it is your sin is 100% true. There’s a verse or Hadith that speaks about that.
It was narrated that Abu Sa’eed Al-Khudri said:
”The Messenger of God (peace be upon him) said: ‘If a person accepts Islam, such that his Islam is good, God will decree reward for every good deed that he did before, and every bad deed that he did before will be erased. Then after that will come the reckoning; each good deed will be rewarded ten times up to seven hundred times. And each bad deed will be recorded as it is, unless God, the Mighty and Sublime, forgives it.'” [Sunan an-Nasa’i]
And also prophet Muhammad (ﷺ ) said:
"Islam wipes out whatever sins came before it" - Ahmad (17159).
But after you have converted to Islam, and you have done a sin, you can seek God’s forgiveness each time you do a mistake or a sin.