Muʽāwiya wrote to Constans II, calling on him to abandon Christianity and turn from Jesus to worship the God of Abraham:

Mu‘āwiya tried to mint gold and silver coins without crosses on them, but this omission meant that people refused to use them (Christians) mainly.

1. See other reports/inscriptions that seem polemical against the cross or a Christian identity: Foss, Arab-Byzantine Coins, p. 118. For the inscription in question, see Y. Hirschfeld, The Roman Baths of Hammat Gader: Final Report (Jerusalem, 1997), pp. 238–40. On this inscription and Mu‘āwiya’s building accomplishments more generally, see D. Whitcomb, ‘Notes for an Archaeology of Mu‘āwiya: Material Culture in the Transitional Period of Believers,’ in A. Borrut and F. M. Donner, eds., Christians and Others in the Umayyad State (Chicago, 2016), pp. 11–27. See also Y. al-Shdaifat, A. Al-Jallad, Z. alSalameen, and R. Harahsheh, ‘An Early Christian Arabic Graffito Mentioning “Yazīd the King,” ’ Arabian Archaeology and Epigraphy 28 (2017), pp. 315–24, for a recently discovered Arabic graffito in Jordan which asks that God remember a certain Yazīd the King.
2. There was, to be sure, negative treatment of the Cross: ‘Why is the Cross being insulted?’ Sophronius asked on Epiphany in 636 or 637, listing a number of unhappy developments that had accompanied the Arab invasions going on even as he preached. Πόθεν σταυρὸς ἐνυβρίζεται; Sophronius of Jerusalem, Homilia in theophaniam 10 (ed. A. Papadopoulos-Kerameus, Analekta hierosolymitikēs stachiologias, vol. 5 [St. Petersburg, 1898], p. 166).

1. ‘Umar’s attempt to build a mosque on the site of the Temple of Solomon in the late 630s or early 640s was reported to have been accompanied by an act of cross removal and a subsequent rise in antagonism toward the Cross throughout the regions of Arab rule: Michael the Great, Chronicle 11.8 (ed. Chabot, 4.421 = 2.431). Theophanes placed ‘Umar’s initial desire to build a sanctuary at the site of Solomon’s Temple in 634–635 (Chronicle AM 6127 [ed. de Boor, vol. 1, p. 339; ET available in Mango and Scott, The Chronicle of Theophanes Confessor, p. 471) and this incident in particular in 642–643 (AM 6135 [ed. de Boor, p. 342 = Mango and Scott, p. 476]), but on these two dates, see C. Mango, ‘The Temple Mount AD 614–638,’ in Raby and Johns, eds., Bayt al-Maqdis, vol. 1, pp. 1–2. Similarly to Mango (p. 2), Flusin, ‘L’esplanade du temple a l’arrivée des Arabes,’ placed the construction of the ‘Mosque of ‘Umar’ around 638. Elias bar Shinaya placed ‘Umar’s building of a mosque on the site of the Temple of Solomon in AH 17/23 January AG 949 (= AD 638)—which was, though he does not note it, the first day of the hijrī year 17 (cf. V. Grumel, La chronologie [Paris, 1958], p. 247); see Elias bar Shinaya, Chronography, pp. 132–33 (ed. E. W. Brooks, Opus chronologicum [CSCO III.7] [Paris, 1910]).
2. There seems to be alot of very, very early Muslim polemical acts & responses to the cross and other Christian distinctive practices, so why should we assume that these groups got salvation according to Muhammad? Most of these are Sahaba, the earliest followers of Muhammad.