Do you have I2C pullup on each i2C line, I've tested the default master/slave examples and it works as expected.

Yes added the the pullup on SDA,SCL again sae issuse

Note

for example in my example wire.write ("Hello/n") it means 6byte are sending after that STM is not working

From the master you can try to read more bytes instead of 6 bytes. If you try more than 6 bytes than STM freezes.
Wire.requestFrom(slave_address,50,true);

Is it a legacy STM32F103?

Yes I am using BLUE PILL (STM32F103C)

This does not mean it is a real STM32, several "bluepill" have a fake STM32.

No. It works on my side with the default examples master/reader. So hard to help on this.

when before sending string, send wire.write(0) then its not freeze

As for this write if its successfully send then return 0 , but in the program getting Len of string 6 only

No, it return ret = quantity as expected. 0 is error.

if have the board try load this code try to read on i2c more than 6 byte than STM is frizzing can plz check it , less than 6 byte working fine but i am requesting more than 6 byte is freezing

#include <Wire.h>

#define I2C_ADDR 8

TwoWire Wire1(PB11,PB10);
void setup()
{
Wire1.begin(I2C_ADDR); // join i2c bus with address #4
Wire1.onRequest(requestEvent); // register event
Wire1.onReceive(receiveEvent); // register event
Serial.begin(115200); // start serial for output
}

void loop()
{
//empty loop
}

// function that executes whenever data is received from master
// this function is registered as an event, see setup()
void receiveEvent(int howMany)
{
while(1 < Wire1.available()) // loop through all but the last
{
char c = Wire1.read(); // receive byte as a character
Serial.print(c); // print the character
}
int x = Wire1.read(); // receive byte as an integer
Serial.println(x); // print the integer
}

// function that executes whenever data is requested by master
// this function is registered as an event, see setup()
void requestEvent()
{
Serial.println( Wire1.print("hello\n")); // respond with message of 6 bytes
// as expected by master
}

Can please check it