How to do random sampling based on customer ID

I have a data set as below

Cust_ID SubDepartment Date Bill_Value 1513 Detergent Bars 20180204 30 1513 French Fries 20180803 160 1513 Fruit Based Juices 20180204 30 1513 Containers 20180803 79 1513 Candies & Lollypops 20180803 165 1513 Cheese 20180204 203.04 1513 Cleaners & Wipers 20180803 159 1513 Chocolates 20180803 448 1513 Frozen Veg Snacks 20180803 570 1860 Salted Biscuits 20180110 40 1860 Oats 20180705 60 1860 Pastries 20180815 198 1860 Cheese 20180110 85 1860 Veg Powdered Soups 20180814 20 1860 Paneer 20180123 99 1860 North Indian Mixes 20180502 59 1860 Flavoured Milk 20180502 40

sample data set

I have want to do random sampling of the data based on customer id such that it picks all the transaction of the selected customers