Surah 49. Al-Hujurat, Ayah 18

This does not mean that we should seek petty motives in newcomers into the House of Islam, That would indeed be habouring suspicions or allowing curiosity to spy out motives, which would be a crime under xlix. 12. We should be true, sincere, and devoted ourselves, and leave the case of others to Allah, from Whose eyes nothing is hidden.