I am a recent revert, coming from Catholicism. I found it quite beautiful to read of people coming from this direction adding the addition of "wa ashadu an na Isa ibn Maryam rasullah"; a sign of respect of the former faith while an affirmation (being the shahadah) of the truth of Islam. What are thoughts on this? Are there preferred formats of how to make this addition, and would one typically only say it sometimes, or during Salah, etc.? Any issues with doing so? There are no issues in saying any mantra that you want, in any language that you want during any time that you want. Because truly it doesn't matter.. Having said that, the "Shahada" by itself is a copied and pasted concept from Catholicism / Orthodoxism, known as "The Apostolic Creed". The Apostolic Creed by itself is a copied and pasted concept from Judaism, known as "The Shema". Whatever Shahada / Creed / Shema that you (or anybody else) wanted to say (or not want to say) is not an issue at all. Because it doesn't matter.. Do it if you feel it will makes you a better man / woman. Your character and deeds.. now those are the things that actually really matters.