Dear Shailesh, Dinesh Divekar has given you sound advice with reasons explained. As a university lecturer, I have used material from various authors and training resources. No doubt, I earned money doing my profession. When in doubt, it's always prudent to write to the author or the publisher and seek their permission, explaining how you use their material. For example, I wrote a few chapters for the book "Managing Total Quality" written by Dr. Hubert Rampersad. For that, I borrowed quite a bit of graphs and displays from various sources. I wrote to the publishers, and they granted permission without any problem.
As you are declaring the source, you are not committing plagiarism; you are really giving free advertisement. Hence, as Dinesh Divekar has suggested, please get their permission to avoid committing copyright violation.