The story of Śrāvaka Devchand and his wife Sushilā is a popular Jain śrāvaka–śrāvikā ideal couple story, but it is not limited to one single original “main” book.

It usually appears in:

• Jain bal-kathā / moral story books
• Vrat-kathā collections (stories told to explain the fruits of good conduct, dān, brahmacharya, etc.)
• General Jain story collections about ideal householders (gṛhastha-jiwan ke आदर्श उदाहरण)

Different authors and publishers include this same basic story with small variations in language and detail. Because of that, the exact combination “Devchand and Sushilā” can be found in many different small Jain story books, and not just one universally-accepted standard granth.

So the accurate reply is:

• There is no single exclusive classical granth that alone contains “the” Devchand–Sushilā story.
• It is a traditional Jain householders’ story, retold in various Jain kathā-sangrahs and children’s story books, especially those teaching ideal gṛhastha life, sacrifice, and right faith.

If you are trying to locate a specific version you have heard (for example from pravachan or pathshala), you will usually find it in:

• “Jain vrat kathā / Jain kathā-sangrah” type small books,
• Or locally printed Jain bal-kathā booklets of your sangh/derasar.